Extreme ultraviolet light generation apparatus

ABSTRACT

An extreme ultraviolet light generation apparatus may include: a chamber including a plasma generation region to which a target is supplied, the target being turned into plasma so that extreme ultraviolet light is generated in the chamber; a target supply part configured to supply the target to the plasma generation region by outputting the target as a droplet into the chamber; a droplet detector configured to detect the droplet traveling from the target supply part to the plasma generation region; an imaging part configured to capture an image of an imaging region containing the plasma generation region in the chamber; and a controller configured to control an imaging timing at which the imaging part captures the image of the imaging region, based on a detection timing at which the droplet detector detects the droplet.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2013-192036, filed Sep. 17, 2013, which is incorporated herein byreference.

BACKGROUND Technical Field

The present disclosure relates to an EUV (extreme ultraviolet) lightgeneration apparatus.

In recent years, as semiconductor processes become finer, transferpatterns for use in photolithographies of semiconductor processes haverapidly become finer. In the next generation, microfabrication at 70 nmto 45 nm, further, microfabrication at 32 nm or less would be demanded.In order to meet the demand for microfabrication at 32 nm or less, forexample, it is expected to develop an exposure apparatus in which asystem for generating EUV light at a wavelength of approximately 13 nmis combined with a reduced projection reflective optical system.

Three types of EUV light generation systems have been proposed, whichinclude an LPP (laser produced plasma) type system using plasmagenerated by irradiating a target material with a laser beam, a DPP(discharge produced plasma) type system using plasma generated byelectric discharge, and an SR (synchrotron radiation) type system usingsynchrotron orbital radiation.

CITATION LIST Patent Literature

PTL1: U.S. Pat. No. 7,087,914

PTL2: U.S. Pat. No. 7,164,144

SUMMARY

According to an aspect of the present disclosure, an extreme ultravioletlight generation apparatus may include: a chamber including a plasmageneration region to which a target is supplied, the target being turnedinto plasma so that extreme ultraviolet light is generated in thechamber; a target supply part configured to supply the target to theplasma generation region by outputting the target as a droplet into thechamber; a droplet detector configured to detect the droplet travelingfrom the target supply part to the plasma generation region; an imagingpart configured to capture an image of an imaging region containing theplasma generation region in the chamber; and a controller configured tocontrol an imaging timing at which the imaging part captures the imageof the imaging region, based on a detection timing at which the dropletdetector detects the droplet.

According to an aspect of the present disclosure, an extreme ultravioletlight generation apparatus configured to generate extreme ultravioletlight, by outputting a target as a droplet to a plasma generation regionin a chamber; and irradiating the target with a laser beam so that thetarget is turned into plasma and emits plasma light may include acontroller configured to cause one imaging part to capture an image ofthe droplet and an image of the plasma light in the plasma generationregion, and to control a position of the droplet and a position of theplasma light, based on the image of the droplet and the image of theplasma light captured by the imaging part.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, selected embodiments of the present disclosure will bedescribed with reference to the accompanying drawings by way of example.

FIG. 1 schematically shows the configuration of an exemplary LPP typeEUV light generation system;

FIG. 2 shows the configuration of an EUV light generation apparatusincluding an image measurement unit;

FIG. 3 shows the configuration of an image measurement system of the EUVlight generation apparatus;

FIG. 4 is a flowchart explaining the outline of the operation of the EUVlight generation apparatus including the image measurement unit;

FIG. 5 shows the configuration of an image measurement system of an EUVlight generation apparatus according to Embodiment 1;

FIG. 6 is a time chart for the image measurement of a droplet by acontroller shown in FIG. 5;

FIG. 7 is a time chart for the image measurement of plasma light by thecontroller shown in FIG. 5;

FIG. 8 is a flowchart explaining a process for image measurement by ashooting controller shown in FIG. 5;

FIG. 9 is a flowchart explaining a process for measuring the image of adroplet by the shooting controller shown in FIG. 5;

FIG. 10A is a flowchart explaining a process for calculating theparameters of a droplet by the shooting controller shown in FIG. 5;

FIG. 10B shows an exemplary image of a droplet captured by an imagingpart of an image measurement unit shown in FIG. 5;

FIG. 11 is a flowchart explaining a process for measuring the image ofplasma light by the shooting controller shown in FIG. 5;

FIG. 12A is a flowchart explaining a process for calculating theparameters of plasma light by the shooting controller shown in FIG. 5;

FIG. 12B shows an exemplary image of the plasma light captured by theimaging part of the image measurement unit shown in FIG. 5;

FIG. 13 shows the configuration of a shooting system using the EUV lightgeneration apparatus according to Embodiment 2;

FIG. 14 is a flowchart explaining a process for shooting control by theshooting controller shown in FIG. 13;

FIG. 15A is a flowchart explaining a process for calculating the targetposition of a droplet by the shooting controller shown in FIG. 13;

FIG. 15B is a drawing explaining the process shown in FIG. 15A;

FIG. 16 is a flowchart explaining a process for setting the targetposition of a droplet, and the target focused position of a pulsed laserbeam by the shooting controller shown in FIG. 13;

FIG. 17 is a flowchart explaining a process for controlling the positionof a droplet by the shooting controller shown in FIG. 13;

FIG. 18 is a flowchart explaining a process for measuring the image of adroplet by the shooting controller shown in FIG. 13;

FIG. 19 is a flowchart explaining a process for calculating the positionof a droplet by the shooting controller shown in FIG. 13;

FIG. 20 is a flowchart explaining a process for controlling the focusedposition of a pulsed laser beam by the shooting controller shown in FIG.13;

FIG. 21 is a flowchart explaining a process for measuring the image ofplasma light by the shooting controller shown in FIG. 13;

FIG. 22 is a flowchart explaining a process for calculating the positionof plasma light by the shooting controller shown in FIG. 13;

FIG. 23A is a drawing showing the relationship of the focused positionof a pulsed laser beam and the position of a droplet, with the positionof plasma light, where the focused position of the pulsed laser beammatches the position of the droplet;

FIG. 23B is a drawing showing the relationship of the focused positionof a pulsed laser beam and the position of a droplet, with the positionof plasma light, where the focused position of the pulsed laser beam isshifted from the position of the droplet in a −Y direction;

FIG. 23C is a drawing showing the relationship of the focused positionof a pulsed laser beam and the position of a droplet, with the positionof plasma light, where the focused position of the pulsed laser beam isshifted from the position of the droplet in a +Y direction;

FIG. 24 shows the configuration of the EUV light generation apparatusaccording to Embodiment 3;

FIG. 25 shows the configuration of the shooting system using the EUVlight generation apparatus according to Embodiment 3;

FIG. 26A shows the state in which the form of a droplet is changed byirradiating the droplet with a main pulse laser beam or a prepulse laserbeam, where the droplet just before being irradiated with the prepulselaser beam is shown;

FIG. 26B shows the state in which the form of a droplet is changed byirradiating the droplet with a main pulse laser beam or a prepulse laserbeam, where the droplet just after being irradiated with the prepulselaser beam is shown;

FIG. 26C shows the state in which the form of a droplet is changed byirradiating the droplet with a main pulse laser beam or a prepulse laserbeam, where a secondary target just before being irradiated with themain pulse laser beam is shown;

FIG. 26D shows the state in which the form of a droplet is changed byirradiating the droplet with a main pulse laser beam or a prepulse laserbeam, where the secondary target just after being irradiated with themain pulse laser beam is shown;

FIG. 27 is a time chart for the image measurement of a droplet by thecontroller shown in FIG. 25;

FIG. 28 is a time chart for the image measurement of a secondary targetby the controller shown in FIG. 25;

FIG. 29 is a time chart for the image measurement of plasma light by thecontroller shown in FIG. 25;

FIG. 30 is a flowchart explaining a process for shooting control by theshooting controller shown in FIG. 25;

FIG. 31A is a flowchart explaining a process for calculating the targetposition of a droplet and the target position of a secondary target bythe shooting controller shown in FIG. 25;

FIG. 31B is a drawing explaining the process shown in FIG. 31A;

FIG. 32 is a flowchart explaining a process for setting the targetposition of a droplet and the target focused positions of a prepulselaser beam and a main pulse laser beam by the shooting controller shownin FIG. 25;

FIG. 33 is a flowchart explaining a process for controlling the positionof a droplet by the shooting controller shown in FIG. 25;

FIG. 34 is a flowchart explaining a process for measuring the image of adroplet by the shooting controller shown in FIG. 25;

FIG. 35 is a flowchart explaining a process for controlling the positionof a secondary target by the shooting controller shown in FIG. 25;

FIG. 36 is a flowchart explaining a process for measuring the image of asecondary target by the shooting controller shown in FIG. 25;

FIG. 37 is a flowchart explaining a process for calculating the positionof a secondary target by the shooting controller shown in FIG. 25;

FIG. 38A is a drawing showing the relationship of the focused positionof a prepulse laser beam and the position of a droplet, with theposition of a secondary target, where the focused position of theprepulse laser beam matches the position of the droplet;

FIG. 38B is a drawing showing the relationship of the focused positionof a prepulse laser beam and the position of a droplet, with theposition of a secondary target, where the focused position of theprepulse laser beam is shifted from the position of the droplet in the−Y direction;

FIG. 38C is a drawing showing the relationship of the focused positionof a prepulse laser beam and the position of a droplet, with theposition of a secondary target, where the focused position of theprepulse laser beam is shifted from the position of the droplet in the+Y direction;

FIG. 39A is a flowchart explaining a process for controlling the focusedposition of a main pulse laser beam by the shooting controller shown inFIG. 25;

FIG. 39B is a flowchart explaining the process continuing from theprocess shown in FIG. 39A;

FIG. 40 is a flowchart explaining a process for measuring the image ofplasma light by the shooting controller shown in FIG. 25;

FIG. 41A is a drawing showing the relationship of the focused positionof a main pulse laser beam and the position of a secondary target, withthe position of plasma light, where the focused position of the mainpulse laser beam matches the position of the secondary target;

FIG. 41B is a drawing showing the relationship of the focused positionof a main pulse laser beam and the position of a secondary target, withthe position of plasma light, where the focused position of the mainpulse laser beam is shifted from the position of the secondary target inthe −Y direction;

FIG. 41C is a drawing showing the relationship of the focused positionof a main pulse laser beam and the position of a secondary target, withthe position of plasma light, where the focused position of the mainpulse laser beam is shifted from the position of the secondary target inthe +Y direction;

FIG. 42A is a drawing showing the relationship between a first prepulselaser beam and the form of the target to be irradiated with the firstprepulse laser beam;

FIG. 42B is a drawing showing the relationship between a second prepulselaser beam and the form of the target to be irradiated with the secondprepulse laser beam;

FIG. 42C is a drawing showing the relationship between a main pulselaser beam and the form of the target to be irradiated with the mainpulse laser beam;

FIG. 42D is a drawing explaining plasma light emitted from the targethaving been irradiated with the main pulse laser beam;

FIG. 43 is the configuration of the shooting system using the EUV lightgeneration apparatus according to Embodiment 4;

FIG. 44A is a drawing showing the state of a droplet just before beingirradiated with a first prepulse laser beam;

FIG. 44B is a drawing showing the state of the droplet just after beingirradiated with the first prepulse laser beam;

FIG. 44C is a drawing showing the state of a secondary target justbefore being irradiated with a second prepulse laser beam;

FIG. 44D is a drawing showing the state of a tertiary target just beforebeing irradiated with a main pulse laser beam;

FIG. 44E is a drawing showing the state of plasma light emitted from thetertiary target just after being irradiated with the main pulse laserbeam;

FIG. 45 is a time chart for the image measurement by the controllershown in FIG. 43, where the image of a droplet is measured just beforethe droplet is irradiated with a first prepulse laser beam;

FIG. 46 is a time chart for the image measurement by the controllershown in FIG. 43, where the image of a secondary target is measured justbefore the secondary target is irradiated with a second prepulse laserbeam;

FIG. 47 is a time chart for the image measurement by the controllershown in FIG. 43, where the image of a tertiary target is measured justbefore the tertiary target is irradiated with a main pulse laser beam;

FIG. 48 is a time chart for the image measurement by the controllershown in FIG. 43, where the image of plasma light emitted from thetertiary target is measured just after the tertiary target is irradiatedwith the main pulse laser beam;

FIG. 49 is a drawing showing the configuration of the image measurementunit of the EUV light generation apparatus according to Embodiment 5;

FIG. 50A is a drawing showing the result of the measurement by a linesensor when a droplet is placed in a proper position in the plasmageneration region;

FIG. 50B is a drawing showing the result of the measurement by a linesensor when the droplet is placed in the proper position in the plasmageneration region;

FIG. 51A is a drawing showing the result of the measurement by the linesensor when the droplet is placed out of the proper position in theplasma generation region;

FIG. 51B is a drawing showing the result of the measurement by the linesensor when the droplet is placed out of the proper position in theplasma generation region;

FIG. 52 is a block diagram showing the hardware environment of eachcontroller; and

FIG. 53 shows the configuration of a shutter.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

<Contents>

1. Overview

2. Description of terms

3. Overview of the EUV light generation system

3.1 Configuration

3.2 Operation

4. EUV light generation apparatus including an image measurement unit

4.1 Configuration

4.2 Operation

4.3 Problem

5. Image measurement system of the EUV light generation apparatusaccording to Embodiment 1

5.1 Configuration

5.2 Operation

5.3 Effect

6. Shooting system using the EUV light generation apparatus according toEmbodiment 2

6.1 Configuration

6.2 Operation

6.3 Effect

7. Shooting system using the EUV light generation apparatus according toEmbodiment 3

7.1 Configuration

7.2 Operation

7.3 Effect

8. Shooting system using the EUV light generation apparatus according toEmbodiment 4

8.1 Configuration

8.2 Operation

8.3 Effect

9. Image measurement unit included in the EUV light generation apparatusaccording to Embodiment 5

9.1 Configuration

9.2 Operation

9.3 Effect

10. Others

10.1 Hardware environment of each controller

10.2 Configuration of shutter

10.3 Another modification

Hereinafter, selected embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Theembodiments to be described below are merely illustrative in nature anddo not limit the scope of the present disclosure. Further, theconfiguration(s) and operation(s) described in each embodiment are notall essential in implementing the present disclosure. Correspondingelements are referenced by corresponding reference numerals andcharacters, and therefore duplicate descriptions will be omitted.

1. Overview

The present disclosure may at least disclose the following embodiments.

An EUV light generation apparatus 1 according to the present disclosuremay include a chamber 2 including a plasma generation region 25 to whicha target 27 is supplied, the target 27 being turned into plasma so thatEUV light 252 is generated in the chamber 2; a target supply part 26configured to supply the target 27 to the plasma generation region 25 byoutputting the target 27 as a droplet 271 into the chamber 2; a dropletdetector 41 configured to detect the droplet 271 traveling from thetarget supply part 26 to the plasma generation region 25; an imagingpart 422 configured to capture an image of an imaging region 25 acontaining the plasma generation region 25 in the chamber 2; and acontroller 8 configured to control an imaging timing at which theimaging part 422 captures the image of the imaging region 25 a, based onthe detection timing at which the droplet detector 41 detects thedroplet 271. Therefore, the EUV light generation apparatus 1 accordingto the present disclosure can precisely measure the states of thedroplet 271 and the plasma light in the plasma generation region 25.

2. Description of Terms

“Target” refers to a substance which is introduced into the chamber andis irradiated with a laser beam. The target irradiated with the laserbeam is turned into plasma and emits EUV light. “Droplet” refers to oneform of the target introduced into the chamber. “State of a droplet”refers to a dynamic state such as the form, the size, and the speed of adroplet outputted from the target supply part into the chamber.“Parameters of a droplet” refers to the physical quantities representingthe state of the droplet. Particularly, the parameters include the size,the position and so forth of the droplet traveling through the chamber.“Plasma light” means the light emitted from the droplet having beenturned into plasma. This emitted light contains EUV light. “State ofplasma light” means the dynamic state such as the form and the size ofplasma light, or the optical state such as the emission intensity, theemission intensity distribution, and the wavelength distribution ofplasma light. “Parameters of plasma light” refers to the physicalquantities representing the state of plasma light. Particularly, theparameters include the size, the position and so forth of plasma light.

3. Overview of the EUV Light Generation System

3.1 Configuration

FIG. 1 schematically shows the configuration of an exemplary LPP typeEUV light generation system. The EUV light generation apparatus 1 may beused with at least one laser device 3. In the present disclosure, thesystem including the EUV light generation apparatus 1 and the laserdevice 3 is referred to as an EUV light generation system 11. As shownin FIG. 1, and as described in detail later, the EUV light generationapparatus 1 may include the chamber 2 and the target supply part 26. Thechamber 2 may be sealed airtight. The target supply part 26 may bemounted onto the chamber 2, for example, to penetrate the wall of thechamber 2. A target material to be supplied from the target supply part26 may include, but is not limited to, tin, terbium, gadolinium,lithium, xenon, or a combination of any two or more of them.

The chamber 2 may have at least one through-hole in its wall. A window21 may be provided on the through-hole. A pulsed laser beam 32 outputtedfrom the laser device 3 may transmit through the window 21. In thechamber 2, an EUV collector mirror 23 having a spheroidal reflectivesurface may be provided. The EUV collector mirror 23 may have a firstfocal point and a second focal point. The surface of the EUV collectormirror 23 may have a multi-layered reflective film in which molybdenumlayers and silicon layers are alternately laminated, for example. TheEUV collector mirror 23 may be preferably arranged such that a firstfocal point is positioned in the plasma generation region 25 and asecond focal point is positioned in an intermediate focus (IF) point292. The EUV collector mirror 23 may have a through-hole 24 formed atthe center thereof so that a pulsed laser beam 33 may pass through thethrough-hole 24.

The EUV light generation apparatus 1 may include an EUV light generationcontroller 5 and a target sensor 4. The target sensor 4 may have animaging function and detect the presence, trajectory, position and speedof the target 27.

Further, the EUV light generation apparatus 1 may include a connectionpart 29 that allows the interior of the chamber 2 to be in communicationwith the interior of an exposure apparatus 6. In the connection part 29,a wall 291 having an aperture 293 may be provided. The wall 291 may bepositioned such that the second focal point of the EUV collector mirror23 lies in the aperture 293.

The EUV light generation apparatus 1 may further include a laser beamdirection control unit 34, a laser beam collector mirror 22, and atarget collector 28 for collecting the target 27. The laser beamdirection control unit 34 may include an optical element for definingthe traveling direction of the laser beam and an actuator for adjustingthe position or the posture of the optical element.

3.2 Operation

With reference to FIG. 1, a pulsed laser beam 31 outputted from thelaser device 3 may pass through the laser beam direction control unit34, transmit through the window 21 as the pulsed laser beam 32, and thenenter the chamber 2. The pulsed laser beam 32 may travel through thechamber 2 along at least one laser beam path, be reflected from thelaser beam collector mirror 22, and be emitted to at least one target 27as the pulsed laser beam 33.

The target supply part 26 may be configured to output the target 27 tothe plasma generation region 25 in the chamber 2. The target 27 may beirradiated with at least one pulse of the pulsed laser beam 33. Uponbeing irradiated with the pulsed laser beam, the target 27 may be turnedinto plasma, and EUV light 251 may be emitted from the plasma togetherwith the emission of light at different wavelengths. The EUV light 251may be selectively reflected from the EUV collector mirror 23. EUV light252 reflected from the EUV collector mirror 23 may be focused on the IFpoint 292, and outputted to the exposure apparatus 6. Here, one target27 may be irradiated with multiple pulses of the pulsed laser beam 33.

The EUV light generation controller 5 may be configured to totallycontrol the EUV light generation system 11. The EUV light generationcontroller 5 may be configured to process the image data and so forth ofthe target 27 captured by the target sensor 4. Further, the EUV lightgeneration controller 5 may be configured to control at least one of:the timing at which the target 27 is outputted; and the direction inwhich the target 27 is outputted. Furthermore, the EUV light generationcontroller 5 may be configured to control at least one of: the timing atwhich the laser device 3 oscillates; the traveling direction of thepulsed laser beam 32; and the position on which the pulsed laser beam 33is focused. The various controls described above are merely examples,and other controls may be added as necessary.

4. EUV Light Generation Apparatus Including an Image Measurement Unit

4.1 Configuration

With reference to FIGS. 2 and 3, the configuration of the EUV lightgeneration apparatus 1 including an image measurement unit 42 will bedescribed. In FIG. 2, the direction in which the EUV light 252 isoutputted from the chamber 2 in the EUV light generation apparatus 1 tothe exposure apparatus 6 is defined as a Z-axis. An X-axis and a Y-axisare orthogonal to the Z-axis, and are orthogonal to one another. Thesame definition of these coordinate axes will be applied to the otherdrawings described later.

The chamber 2 of the EUV light generation apparatus 1 may be formedinto, for example, a hollow spherical shape or a hollow cylindricalshape. The direction of the central axis of the cylindrical chamber 2may be the same as the direction in which the EUV light 252 is outputtedto the exposure apparatus 6.

The cylindrical chamber 2 may include a target supply passage 2 a formedon its side surface, for supplying the target 27 into the chamber 2 fromthe outside of the chamber 2. The target supply passage 2 a may beformed in a cylindrical shape. A target supply hole 2 b may be formed inthe front end of the target supply passage 2 a. The direction of thecentral axis of the cylindrical target supply passage 2 a may beorthogonal to the direction in which the EUV light 252 is outputted tothe exposure apparatus 6. If the chamber 2 is formed into a hollowspherical shape, the target supply passage 2 a may be formed on the wallsurface of the chamber 2 at a position in which the window 21 and theconnection part 29 are not provided.

In the chamber 2, a laser beam focusing optical system 22 a, an EUVlight focusing optical system 23 a, the target collector 28, a plate225, a plate 235, and a triaxial stage 226 may be provided.

The plate 235 may be fixed to the inner side surface of the chamber 2. Ahole 235 a that allows the pulsed laser beam 33 to pass therethrough maybe formed at the center of the plate 235 in the thickness direction ofthe plate 235. The opening direction of the hole 235 a may be the sameas the direction of the axis passing through the through-hole 24 and theplasma generation region 25 shown in FIG. 1.

The EUV light focusing optical system 23 a may be provided on onesurface of the plate 235. Meanwhile, on the other surface of the plate235, the plate 225 may be provided via the triaxial stage 226.

The EUV light focusing optical system 23 a provided on the one surfaceof the plate 235 may include the EUV collector mirror 23 and a holder231. The holder 231 may hold the EUV collector mirror 23. The holder 231holding the EUV collector mirror 23 may be fixed to the plate 235.

The plate 225 provided on the other surface of the plate 235 may bechanged in its position and posture by the triaxial stage 226. Thetriaxial stage 226 may move the plate 225 in the triaxial directions ofX, Y, and Z. The triaxial stage 226 may be connected to a shootingcontroller 81 described later. The triaxial stage 226 may move the plate225 according to a control signal from the shooting controller 81. Bythis means, the position and the posture of the plate 225 may bechanged. The laser beam focusing optical system 22 a may be provided onthe plate 225.

The laser beam focusing optical system 22 a may include the laser beamcollector mirror 22, a holder 223 and a holder 224. The laser beamcollector mirror 22 may include an off-axis paraboloidal mirror 221 anda plane mirror 222.

The holder 223 may hold the off-axis paraboloidal mirror 221. The holder223 holding the off-axis paraboloidal mirror 221 may be fixed to theplate 225. The holder 224 may hold the plane mirror 222. The holder 224holding the plane mirror 222 may be fixed to the plate 225.

The off-axis paraboloidal mirror 221 may be placed to face each of thewindow 21 provided on the bottom surface of the chamber 2 and the planemirror 222. The plane mirror 222 may be placed to face each of the hole235 a and the off-axis paraboloidal mirror 221. The shooting controller81 changes the position and posture of the plate 225 via the triaxialstage 226, so that it is possible to adjust the positions and posturesof the off-axis paraboloidal mirror 221 and the plane mirror 222. Thisadjustment may be performed such that the pulsed laser beam 33, which isa reflected beam of the pulsed laser beam 32 having entered the off-axisparaboloidal mirror 221 and the plane mirror 222, is focused on theplasma generation region 25.

The target collector 28 may be positioned on the extension of thetraveling direction of the droplet 271 outputted into the chamber 2.

Meanwhile, the laser beam direction control unit 34, the EUV lightgeneration controller 5, the target generator 7, the droplet detector41, the image measurement unit 42, and the controller 8 may be providedoutside the chamber 2. The controller 8 may include the shootingcontroller 81 and a delay circuit 82.

The laser beam direction control unit 34 may be provided between thewindow 21 formed on the bottom surface of the chamber 2 and the laserdevice 3. The laser beam direction control unit 34 may include ahigh-reflection mirror 341, a high-reflection mirror 342, a holder 343and a holder 344.

The holder 343 may hold the high-reflection mirror 341. The holder 344may hold the high-reflection mirror 342. The positions and postures ofthe holders 343 and 344 may be changed by an actuator (not shown) whichis connected to the EUV light generation controller 5.

The high-reflection mirror 341 may be placed to face each of the exitaperture of the laser device 3 from which the pulsed laser beam 31exits, and the high-reflection mirror 342. The high-reflection mirror342 may be placed to face each of the window 21 of the chamber 2 and thehigh-reflection mirror 341. The EUV light generation controller 5changes the positions and postures of the holders 343 and 344, so thatit is possible to adjust the positions and postures of thehigh-reflection mirrors 341 and 342. This adjustment may be performedsuch that the pulsed laser beam 32, which is the reflected beam of thepulsed laser beam 31 having entered the high-reflection mirrors 341 and342, transmits through the window 21 formed on the bottom surface of thechamber 2.

The EUV light generation controller 5 may send/receive control signalsto/from an exposure apparatus controller 61 which is the controller ofthe exposure apparatus 6. By this means, the EUV light generationcontroller 5 may totally control the entire operation of the EUV lightgeneration system 11 according to commands from the exposure apparatus6. The EUV light generation controller 5 may send/receive controlsignals to/from the laser device 3. By this means, the EUV lightgeneration controller 5 may control the operation of the laser device 3.The EUV light generation controller 5 may send/receive control signalsto/from the actuators of the laser beam direction control unit 34 andthe laser beam focusing optical system 22 a. By this means, the EUVlight generation controller 5 may adjust the traveling directions andthe focused positions of the pulsed laser beams 31 to 33. The EUV lightgeneration controller 5 may send/receive control signals to/from theshooting controller 81. By this means, the EUV light generationcontroller 5 may control the operations of the target generator 7, thedroplet detector 41, and the image measurement unit 42. Here, thehardware configuration of the EUV light generation controller 5 will bedescribed later with reference to FIG. 42.

The target generator 7 may be provided on the end of the target supplypassage 2 a of the chamber 2. The target generator 7 may include thetarget supply part 26, a temperature regulating mechanism 71, a pressureregulating mechanism 72, a droplet forming mechanism 73, and a biaxialstage 74.

The target supply part 26 may include a tank 261, and a nozzle 262. Thetank 261 may be formed into a hollow cylindrical shape. The hollow tank261 may accommodate the target 27. At least the interior of the tank 261accommodating the target 27 may be made of a material which is notlikely to react with the target 27. The material which is not likely toreact with the target 27 may be any of, for example, SiC, SiO₂, Al₂O₃,molybdenum, tungsten and tantalum.

The nozzle 262 may be provided on the bottom surface of the cylindricaltank 261. The nozzle 262 may be placed inside the chamber 2 via thetarget supply hole 2 b of the chamber 2. The target supply hole 2 b maybe closed by providing the target supply part 26. By this means, it ispossible to isolate the interior of the chamber 2 from the atmosphere.At least the inner surface of the nozzle 262 may be made of a materialwhich is not likely to react with the target 27.

One end of the pipe-like nozzle 262 may be fixed to the hollow tank 261.A nozzle hole 262 a may be formed in the other end of the pipe-likenozzle 262 as shown in FIG. 3. The tank 261 provided in one end side ofthe nozzle 262 may be placed outside the chamber 2. Meanwhile, thenozzle hole 262 a provided on the other end side of the nozzle 262 maybe placed inside the chamber 2. The plasma generation region 25 placedinside the chamber 2 may be positioned on the extension of the directionof the central axis of the nozzle 262. The interiors of the tank 261,the nozzle 262, the target supply passage 2 a, and the chamber 2 maycommunicate with each other. The nozzle hole 262 a may be formed into ashape that allows the molten target 27 to be jetted into the chamber 2.

The temperature regulating mechanism 71 may regulate the temperature ofthe tank 261. As shown in FIG. 3, the temperature regulating mechanism71 may include a heater 711 and a heater power source 712.

The heater 711 may be fixed to the outer side surface of the cylindricaltank 261. The heater 711 fixed to the tank 261 may heat the tank 261.The heater 711 that heats the tank 261 may be connected to the heaterpower source 712. The heater power source 712 may supply electric powerto the heater 711. The heater power source 712 that supplies electricpower to the heater 711 may be connected to the shooting controller 81.The power supply from the heater power source 712 to the heater 711 maybe controlled by the shooting controller 81.

A temperature sensor (not shown) may be fixed to the outer side surfaceof the cylindrical tank 261. The temperature sensor fixed to the tank261 may be connected to the shooting controller 81. The temperaturesensor may detect the temperature of the tank 261 and output a detectionsignal to the shooting controller 81. The shooting controller 81 mayregulate the electric power to be supplied to the heater 711, based onthe detection signal outputted from the temperature sensor.

With the above-described configuration, the temperature regulatingmechanism 71 can regulate the temperature of the tank 261, according tothe control signal from the shooting controller 81.

The pressure regulating mechanism 72 may regulate the pressure in thetank 261. As shown in FIG. 3, the pressure regulating mechanism 72 mayinclude a pressure regulator 721, a pipe 722, and a gas bomb 723.

The pipe 722 may connect between the bottom surface of the cylindricaltank 261 in the opposite side of the nozzle 262 and the pressureregulator 721. The pipe 722 allows the communication between the targetsupply part 26 including the tank 261 and the pressure regulator 721.The pipe 722 may be covered with, for example, a heat insulatingmaterial (not shown). A heater (not shown) may be provided at the pipe722. The temperature in the pipe 722 may be maintained at the sametemperature as the temperature in the tank 261 of the target supply part26.

The gas bomb 723 may be filled with inert gas such as helium, argon andso forth. The gas bomb 723 may supply the inert gas into the tank 261via the pressure regulator 721.

As described above, the pressure regulator 721 may be provided on thebottom surface of the cylindrical tank 261 in the opposite side of thenozzle 262 via the pipe 722. The pressure regulator 721 may include, forexample, a solenoid valve for air supply and air exhaust, and a pressuresensor. The pressure regulator 721 may detect the pressure in the tank261 by using the pressure sensor. The pressure regulator 721 may beconnected to the gas bomb 723. The pressure regulator 721 may supply theinert gas contained in the gas bomb 723 into the tank 261. The pressureregulator 721 may be connected to an exhaust pump (not shown). Thepressure regulator 721 may activate the exhaust pump to exhaust the gasfrom the tank 261. The pressure regulator 721 may supply the gas intothe tank 261 or exhaust the gas from the tank 261, and therefore toincrease or reduce the pressure in the tank 261.

The pressure regulator 721 may be connected to the shooting controller81. The pressure regulator 721 may output the detection signalindicating the detected pressure to the shooting controller 81. Thecontrol signal outputted from the shooting controller 81 may be inputtedto the pressure regulator 721. The control signal outputted from theshooting controller 81 may be a control signal for controlling theoperation of the pressure regulator 721 such that the pressure in thetank 261 is a target pressure, according to the detection signaloutputted from the pressure regulator 721. The pressure regulator 721may supply the gas into the tank 261 or exhaust the gas from the tank261, according to the control signal from the shooting controller 81. Bythis means, it is possible to regulate the pressure in the tank 261 atthe target pressure.

With the above-described configuration, the pressure regulatingmechanism 72 can cause the pressure regulator 721 to regulate thepressure in the tank 261, according to the control signal from theshooting controller 81.

The droplet forming mechanism 73 may periodically divide the flow of thetarget 27 jetted from the nozzle 262 to form droplets 271. The dropletforming mechanism 73 may form the droplets 271 by, for example, thecontinuous jet method. With the continuous jet method, a standing wavemay be given to the flow of the jetted target 27 by vibrating the nozzle262 to periodically divide the target 27. The divided target 27 may forma free interface by means of its own surface tension to form a droplet271. As shown in FIG. 3, the droplet forming mechanism 73 may include apiezoelectric element 731 and a piezoelectric power source 732.

The piezoelectric element 731 may be fixed to the outer side surface ofthe pipe-like nozzle 262. The piezoelectric element 731 fixed to thenozzle 262 may cause a vibration of the nozzle 262. The piezoelectricelement 731 that causes a vibration of the nozzle 262 may be connectedto the piezoelectric power source 732. The piezoelectric power source732 may supply electric power to the piezoelectric element 731. Thepiezoelectric power source 732 that supplies electric power to thepiezoelectric element 731 may be connected to the shooting controller81. The power supply from the piezoelectric power source 732 to thepiezoelectric element 731 may be controlled by the shooting controller81.

With the above-described configuration, the droplet forming mechanism 73can form the droplet 271, according to the control signal from theshooting controller 81.

The biaxial stage 74 may move the target supply part 26 in the biaxialdirections of X and Z. The biaxial stage 74 may be connected to theshooting controller 81. The control signal outputted from the shootingcontroller 81 may be inputted to the biaxial stage 74. The controlsignal outputted from the shooting controller 81 may be a control signalfor adjusting the position of the target supply part 26 to allow thedroplet 271 outputted into the chamber 2 to reach the target position.The biaxial stage 74 may move the target supply part 26 according to thecontrol signal from the shooting controller 81. By this means, it ispossible to adjust the position of the droplet 271 outputted into thechamber 2 in the X direction and the Z direction to allow the droplet271 to reach the target position.

The droplet detector 41 may detect the droplet 271 outputted into thechamber 2. As shown in FIG. 2, the droplet detector 41 may be providedon the side surface of the target supply passage 2 a at a predeterminedposition. The droplet detector 41 may be placed between the targetsupply part 26 and the plasma generation region 25.

As shown in FIG. 3, the droplet detector 41 may include a light sourcepart 411 and a light receiving part 412. The light source part 411 andthe light receiving part 412 may be placed to face one another across atarget traveling path 272 through which the target 27 outputted into thechamber 2 travels. The direction in which the light source part 411 andthe light receiving part 412 face one another may be orthogonal to thetarget traveling path 272.

Note that although FIG. 2 shows an arrangement where the light sourcepart 411 and the light receiving part 412 face one another in thedirection orthogonal to the X direction for the sake of convenience, thedirection in which the light source part 411 and the light receivingpart 412 face one another is not limited to that. The light source part411 and the light receiving part 412 may face one another in the Xdirection as shown in FIG. 3.

The light source part 411 may emit continuous light to the droplets 271traveling through the target traveling path 272. The continuous lightemitted to the droplet 271 may be a continuous laser beam. The lightsource part 411 may include a light source 411 a, an illuminationoptical system 411 b, and a window 411 c.

The light source 411 a may be, for example, a CW (continuous wave) laseroscillator which emits a continuous laser beam. The beam diameter of thecontinuous laser beam may be sufficiently greater than the diameter(e.g., 20 μm) of the droplet 271.

The illumination optical system 411 b may be an optical element such asa lens. This lens may be a cylindrical lens. The illumination opticalsystem 411 b may focus the continuous laser beam emitted from the lightsource 411 a on a predetermined position P on the target traveling path272 via the window 411 c.

With the above-described configuration, the light source part 411 canemit the continuous laser beam toward the predetermined position P onthe target traveling path 272. When passing through the predeterminedposition P, the droplet 271 traveling through the target traveling path272 may be irradiated with the continuous laser beam emitted from thelight source part 411.

The light receiving part 412 may receive the continuous laser beamemitted from the light source part 411 and detect the optical intensityof the continuous laser beam. The light receiving part 412 may includean optical sensor 412 a, a light receiving optical system 412 b, and awindow 412 c.

The light receiving optical system 412 b may be an optical system suchas a collimator, or be formed by an optical element such as a lens. Thelight receiving optical system 412 b may guide the continuous laser beamemitted from the light source part 411 to the optical sensor 412 a viathe window 412 c.

The optical sensor 412 a may be a light receiving element including aphotodiode. The optical sensor 412 a may detect the optical intensity ofthe continuous laser beam guided by the light receiving optical system412 b. The optical sensor 412 a may be connected to the shootingcontroller 81. The optical sensor 412 a may output a detection signalindicating the detected optical intensity to the shooting controller 81.

With the above-described configuration, the light receiving part 412 candetect the optical intensity of the continuous laser beam emitted fromthe light source part 411, and output the detection signal to theshooting controller 81. When the droplet 271 passes through thepredetermined position P on the target traveling path 272, the opticalintensity of the continuous laser beam detected by the light receivingpart 412 is reduced because the continuous laser beam is blocked by thedroplet 271. The light receiving part 412 may output a signal responsiveto the reduction in the optical intensity due to the passage of thedroplet 271, to the shooting controller 81. Here, the signal responsiveto the reduction in the optical intensity due to the passage of thedroplet 271 may be referred to as “droplet detection signal.”

With the above-described configuration, the droplet detector 41 candetect the droplet 271 traveling from the target supply part 26 to theplasma generation region 25, and output the droplet detection signal tothe shooting controller 81. By this means, the shooting controller 81can detect the timing at which the droplet 271 traveling from the targetsupply part 26 to the plasma generation region 25 is detected. Inparticular, the shooting controller 81 can detect the timing at whichthe droplet 271 is passing through the predetermined position P on thetarget traveling path 272. Here, the timing at which the dropletdetector 41 detects the droplet 271 may be referred to as “detectiontiming.” The detection timing may be a timing at which the dropletdetector 41 outputs the droplet detection signal to the shootingcontroller 81.

The image measurement unit 42 may capture the image of the plasmageneration region 25 and the vicinity thereof in the chamber 2 andgenerate the image data. The image measurement unit 42 may be providedon the wall surface of the chamber 2 in the vicinity of the plasmageneration region 25.

The image measurement unit 42 may include a light source part 421 and animaging part 422. The light source part 421 and the imaging part 422 maybe placed to face one another across the plasma generation region 25 onthe target traveling path 272. The direction in which the light sourcepart 421 and the imaging part 422 face one another may be orthogonal tothe target traveling path 272.

Note that although FIG. 2 shows an arrangement where the light sourcepart 421 and the imaging part 422 face one another in the directionorthogonal to the X direction for the sake of convenience, the directionin which the light source part 421 and the imaging part 422 face oneanother is not limited to that. The light source part 421 and theimaging part 422 may face one another in the X direction as shown inFIG. 3.

The light source part 421 may emit pulsed light to the droplet 271having traveled through the target traveling path 272 and reaching theplasma generation region 25. The light source part 421 may include alight source 421 a, an illumination optical system 421 b, and a window421 c.

The light source 421 a may be, for example, a xenon flash tube or alaser beam source which performs pulse-lighting. The light source 421 amay be connected to the shooting controller 81. “Lighting signal”outputted from the shooting controller 81 may be inputted to the lightsource 421 a. The lighting signal outputted from the shooting controller81 may be a control signal for controlling the operation of the lightsource 421 a such that the light source 421 a performs pulse-lighting ata predetermined timing. The light source 421 a may emit pulsed lightaccording to the lighting signal from the shooting controller 81.

The illumination optical system 421 b may be an optical system such as acollimator, or be formed by an optical element such as a lens. Theillumination optical system 421 b may guide the pulsed light emittedfrom the light source 421 a to the plasma generation region 25 on thetarget traveling path 272 via the window 421 c.

With the above-described configuration, the light source part 421 canemit light to the plasma generation region 25 on the target travelingpath 272. Upon reaching the plasma generation region 25, the droplet 271having traveled through the target traveling path 272 may be irradiatedwith the pulsed light emitted from the light source part 421.

The imaging part 422 may capture the image of the shadow of the droplet271 irradiated with the pulsed light from the light source part 421. Theimaging part 422 may include an image sensor 422 a, a transfer opticalsystem 422 b and a window 422 c.

The transfer optical system 422 b may be an optical element such as apair of lenses. These lenses may be cylindrical lenses. The transferoptical system 422 b may form the image of the shadow of the droplet 271in the plasma generation region 25, which is guided via the window 422c, on the light receiving surface of the image sensor 422 a.

The image sensor 422 a may be a two-dimensional image sensor such as aCCD (charge-coupled device). The image sensor 422 a may capture theimage of the shadow of the droplet 271, which has been formed by thetransfer optical system 422 b. The image sensor 422 a may include ashutter (not shown). The shutter may be an electric shutter or amechanical shutter. The image sensor 422 a may capture an image onlywhen the shutter (not shown) is open. The image sensor 422 a may beconnected to the shooting controller 81. “Imaging signal” outputted fromthe shooting controller 81 may be inputted to the image sensor 422 a.The imaging signal outputted from the shooting controller 81 may be acontrol signal for controlling the operation of the image sensor 422 asuch that the image sensor 422 a captures the image of the shadow of thedroplet 271 at a predetermined timing. The image sensor 422 a maycapture the image of the shadow of the droplet 271, according to theimaging signal from the shooting controller 81. Then, the image sensor422 a may generate the image data of the image of the shadow of thedroplet 271 captured. The image sensor 422 a may output the generatedimage data to the shooting controller 81.

With the above-described configuration, the imaging part 422 can capturethe image of the shadow of the droplet 271 irradiated with the pulsedlight from the light source part 421, and output the image data to theshooting controller 81.

With the above-described configuration, the image measurement unit 42may output the image data of the droplet 271 reaching the plasmageneration region 25, to the shooting controller 81. By this means, theshooting controller 81 can acquire the image data of the droplet 271reaching the plasma generation region 25. The shooting controller 81 canmeasure the state of the droplet 271 based on the acquired image data.

The shooting controller 81 may send/receive control signals to/from theEUV light generation controller 5. By this means, the shootingcontroller 81 may totally control the operations of the target generator7, the droplet detector 41, and the image measurement unit 42, accordingto the control signals from the EUV light generation controller 5. Theshooting controller 81 may output a control signal to the heater powersource 712 to control the operation of the temperature regulatingmechanism 71 including the heater power source 712. The shootingcontroller 81 may output a control signal to the pressure regulator 721to control the operation of the pressure regulating mechanism 72including the pressure regulator 721. The shooting controller 81 mayoutput a control signal to the piezoelectric power source 732 to controlthe operation of the droplet forming mechanism 73 including thepiezoelectric power source 732. The shooting controller 81 may output acontrol signal to the biaxial stage 74 to control the operation of thebiaxial stage 74. The shooting controller 81 may output a lightingsignal to the light source 421 a to control the operation of the lightsource part 421 including the light source 421 a. The shootingcontroller 81 may output an imaging signal to the image sensor 422 a tocontrol the operation of the imaging part 422 including the image sensor422 a.

Moreover, the shooting controller 81 may be connected to the laserdevice 3 via the delay circuit 82. The shooting controller 81 may outputthe droplet detection signal outputted from the droplet detector 41directly to the delay circuit 82.

The delay circuit 82 may output “trigger signal” to the laser device 3at the timing that is delayed by “delay time Tdl” from when the dropletdetection signal is outputted. The trigger signal outputted from thedelay circuit 82 may be a signal that triggers laser oscillation of thelaser device 3 to output the pulsed laser beam 31. The delay time Tdlmay be defined to synchronize the timing at which the pulsed laser beam33 is focused on the plasma generation region 25 with the timing atwhich the droplet 271 reaches the plasma generation region 25. By thismeans, when the droplet 271 having passed through the predeterminedposition P on the target traveling path 272 reaches the plasmageneration region 25, the droplet 271 can be irradiated with the pulsedlaser beam 33. The shooting controller 81 may set the delay time Tdl inthe delay circuit 82.

The timing at which the droplet 271 is irradiated with the pulsed laserbeam 33 in the plasma generation region 25 may be referred to as“irradiation timing.” The period of time required from when the delaycircuit 82 outputs a trigger signal to the laser device 3 until thepulsed laser beam 33 is focused on the plasma generation region 25 maybe referred to as “time α.” The irradiation timing of the pulsed laserbeam 33 may be a timing having elapsed by “delay time Tdl+time α” fromwhen the droplet detection signal is outputted. By setting the delaytime Tdl in the delay circuit 82, the shooting controller 81 can controlthe irradiation timing of the pulsed laser beam 33, based on thedetection timing of the droplet 271. Here, the hardware configuration ofthe shooting controller 81 will be described later with reference toFIG. 42.

4.2 Operation

With reference to FIG. 4, the outline of the operation of the EUV lightgeneration apparatus 1 including the image measurement unit 42 will bedescribed.

In step S1, the shooting controller 81 may perform initial setting forthe target generator 7, the droplet detector 41, and the imagemeasurement unit 42. The shooting controller 81 may activate thesecomponents and check their operations. Then, the shooting controller 81may initialize each of the components and set an initial setting valuein each of the components.

In particular, the shooting controller 81 may set the initial pressuresetting value of the pressure regulator 721 to make the pressure in thetank 261 have a value in an approximately vacuum state. The pressurevalue in the approximately vacuum state may be, for example, about 1hPa. The gas which is likely to react with the target 27 in the tank 261may be discharged before the target 27 has molten. In this case, theinert gas in the gas bomb 723 may be supplied into the tank 261 severaltimes to purge the tank 261.

Moreover, the shooting controller 81 may set an initial temperaturesetting value of the heater 711 to make the temperature of the target 27have a value equal to or higher than the melting point of the target 27.When the target 27 is tin, the initial temperature setting value of theheater 711 may be, for example, equal to or higher than 232 degreesCelsius and lower than 300 degrees Celsius. Alternatively, the initialtemperature setting value of the heater 711 may be equal to or higherthan 300 degrees Celsius.

In step S2, the shooting controller 81 may control the heating by theheater 711 via the heater power source 712. The target 27 accommodatedin the tank 261 may be heated to a temperature equal to or higher thanits melting point. The heated target 27 may be molten. The shootingcontroller 81 may appropriately correct the temperature setting value tomaintain the temperature of the target 27 within a predetermined rangethat is equal to or higher than the melting point of the target 27. Theshooting controller 81 may control the power supply to the heater 711based on the correction of the temperature setting value.

In step S3, the shooting controller 81 may cause the piezoelectric powersource 732 to supply electric power to the piezoelectric element 731.The piezoelectric element 731 may cause a vibration of the nozzle 262.Here, the shooting controller 81 may control the operation of thepiezoelectric power source 732 to supply the electric power having apredetermined waveform to the piezoelectric element 731. Thispredetermined waveform may be a waveform to generate the droplets 271 ata predetermined generation frequency. The predetermined generationfrequency may be, for example, from 50 kHz to 100 kHz.

In step S4, the shooting controller 81 may set a pressure setting valuein the pressure regulator 721, which allows the pressure in the tank 261to be able to supply the target 27. The pressure regulator 721 mayregulate the pressure in the tank 261 at the pressure setting value setas above. The pressure at which the target 27 can be supplied may be apressure at which a constant amount of the molten target 27 jets fromthe nozzle hole 262 a and reaches the plasma generation region 25 at apredetermined speed. The pressure may be applied to the molten target 27accommodated in the tank 261. The target 27 under pressure may flow fromthe tank 261 to the nozzle 262, and a constant amount of the target 27may be jetted from the nozzle hole 262 a. The constant amount of thetarget 27 jetted may be vibrated by the piezoelectric element 731 for aconstant cycle, so that it is possible to form the uniform droplet 271for the constant cycle. The formed droplets 271 may be outputted intothe chamber 2. Here, the cycle for which the droplet 271 is outputtedfrom the target supply part 26 into the chamber 2 may be referred to as“generation cycle” of the droplet 271.

In step S5, the shooting controller 81 may detect the droplet 271outputted into the chamber 2. The droplet detector 41 may output adroplet detection signal to the shooting controller 81. When the droplet271 is outputted for a predetermined generation cycle, the dropletdetection signal may be outputted to the shooting controller 81 for thesame cycle as the predetermined generation cycle. By receiving thedroplet detection signal, the shooting controller 81 may detect thedroplet 271. To be more specific, the shooting controller 81 may detectthat the droplet 271 outputted into the chamber 2 is passing through thepredetermined position P on the target traveling path 272.

In step S6, the shooting controller 81 may set a delay time. Theshooting controller 81 may output the inputted droplet detection signalto the delay circuit 82 to set the delay time Tdl. The delay circuit 82may output a trigger signal to the laser device 3 at a timing that isdelayed from the inputted droplet detection signal by the delay timeTdl. The laser device 3 may oscillate and output the pulsed laser beam31. The pulsed laser beam 31 outputted from the laser device 3 may beintroduced into the chamber 2 as a pulsed laser beam 32, via the laserbeam direction control unit 34. The pulsed laser beam 32 introduced intothe chamber 2 may be focused by the laser beam focusing optical system22 a, and guided to the plasma generation region 25 as a pulsed laserbeam 33.

In step S7, the shooting controller 81 may capture the image of thedroplet 27 a reaching the plasma generation region 25. The droplet 271outputted into the chamber 2 may pass through the predetermined positionP on the target traveling path 272, and then reach the plasma generationregion 25. The shooting controller 81 may capture the image of thedroplet 271 just before being irradiated with the pulsed laser beam 33.

In step S8, the shooting controller 81 may capture the image of plasmalight. When the timing at which the droplet 271 reaches the plasmageneration region 25 is synchronized with the irradiation timing of thepulsed laser beam 33, the droplet 271 is irradiated with the pulsedlaser beam 33. The droplet 271 irradiated with the pulsed laser beam 33may be turned into plasma. The droplet 271 turned into plasma may emitplasma light containing the EUV light 251. The shooting controller 81may capture the image of the plasma light emitted from the droplet 271just after being irradiated with the pulsed laser beam 33.

4.3 Problem

The EUV light generation apparatus 1 may output a plurality of droplets271 into the chamber 2. It is preferred that each of the plurality ofdroplets 271 is in a certain state in the plasma generation region 25.Likewise, it is also preferred that the plasma light emitted from thedroplet 271 having been turned into plasma is in a certain state in theplasma generation region 25. Therefore, there is a demand for technologythat can precisely measure the states of the droplet 271 and the plasmalight in the plasma generation region 25, and can correctly recognizethat the droplet 271 and the plasma light are in the certain states,respectively.

With the EUV light generation apparatus 1 configured to output the EUVlight 252 at a high repetition frequency, the plasma light having a highoptical intensity may be repeatedly emitted for a significantly shortcycle. The generation cycle of the droplet 271 may be significantlyshort, for example, about 10 μs. When the droplet 271 is irradiated withthe pulsed laser beam 33 every time the droplet 271 reaches the plasmageneration region 25, the cycle for which the plasma light is emittedmay be significantly short, for example, about 10 μs. Therefore, thereis a demand for a technology that can precisely control the timing atwhich the droplet 271 reaches the plasma generation region 25, theimaging timing of the imaging part 422, and the irradiation timing ofthe pulsed laser beam 33.

In particular, when the image of plasma light is captured during theoperation of the EUV light generation apparatus 1, some phenomena, suchas smearing and blooming occur. The smearing is a phenomenon in whichunnecessary saturated charge generated by plasma light having a highoptical intensity is mixed into the charge transfer process of the CCDof the image sensor 422 a. The blooming is a phenomenon in whichunnecessary saturated charge generated by plasma light having a highoptical intensity overflows from a proper pixel and flows into anadjacent pixel. If these phenomena occur, the unnecessary saturatedcharge appears in the image as a noise, and it makes it difficult toprecisely measure the state of the plasma light. Therefore, in order tomeasure the droplet 271 and the plasma light in the plasma generationregion 25, there is a demand for a technology that can precisely controlthe above-described timings.

Moreover, if an image measurement unit for performing image measurementby capturing the image of plasma light is provided separately from animage measurement unit for performing image measurement by capturing theimage of the droplet 271, the EUV light generation apparatus 1 becomescomplicated and the cost is increased. Therefore, there is a demand fora technology that can measure the states of the droplet 271 and theplasma light in the plasma generation region 25 by one image measurementunit while the EUV light generation apparatus 1 is operated.

5. Image Measurement System Included in the EUV Light GenerationApparatus According to Embodiment 1

5.1 Configuration

Now, the configuration of the image measurement system included in theEUV light generation apparatus 1 according to Embodiment 1 will bedescribed with reference to FIG. 5. The image measurement systemincluded in the EUV light generation apparatus 1 according to Embodiment1 may include the target generator 7, the droplet detector 41, the imagemeasurement unit 42, and the controller 8. The controller 8 may includethe shooting controller 81, the delay circuit 82, and an imagemeasurement control circuit 83. The configuration of the imagemeasurement system shown in FIG. 5, which is the same as theconfiguration of the EUV light generation apparatus 1 shown in FIGS. 2and 3, will not be described again here.

The configurations of the target generator 7 and the droplet detector 41shown in FIG. 5 may be the same as those of the target generator 7 andthe droplet detector 41 shown in FIGS. 2 and 3.

The image measurement unit 42 shown in FIG. 5 may measure the image ofthe droplet 271 reaching the plasma generation region 25. The imagemeasurement unit 42 may measure the image of the plasma light emitted inthe plasma generation region 25. The image measurement unit 42 mayinclude the light source part 421 and the imaging part 422. The lightsource part 421 and the imaging part 422 may be placed to face oneanother across the plasma generation region 25 on the target travelingpath 272. The direction in which the light source part 421 and theimaging part 422 face one another may be orthogonal to the targettraveling path 272.

The light source part 421 may include a light source 421 a, anillumination optical system 421 b, and a window 421 c.

The light source 421 a may be connected to the shooting controller 81via the image measurement control circuit 83. A lighting signaloutputted from the image measurement control circuit 83 may be inputtedto the light source 421 a. The lighting signal outputted from the imagemeasurement control circuit 83 may be a control signal for controllingthe operation of the light source 421 a such that the light source 421 aperforms pulse-lighting at a predetermined timing. The light source 421a may emit pulsed light according to the lighting signal outputted fromthe image measurement control circuit 83.

The other configuration of the light source 421 a may be the same asthat of the light source 421 a shown in FIG. 3. Moreover, theconfigurations of the illumination optical system 421 b and the window421 c may be the same as those of the illumination optical system 421 band the window 421 c shown in FIG. 3.

The imaging part 422 may capture the image of the imaging region 25 a.The imaging region 25 a may be a predetermined region including theplasma generation region 25 in the chamber 2. The center of the imagingregion 25 a may be located on the target traveling path 272. The size ofthe imaging region 25 a may be sufficiently greater than the size ofeach of the plasma generation region 25, the droplet 271, and the plasmalight. The droplet 271 reaching the plasma generation region 25 may fallwithin the imaging region 25 a. The plasma light emitted in the plasmageneration region 25 may fall within the imaging region 25 a. That is,the imaging part 422 may capture the images of the droplet 271 and theplasma light in the plasma generation region 25.

The imaging part 422 may include the image sensor 422 a, the transferoptical system 422 b, the window 422 c, and a shutter 422 d.

The image sensor 422 a may be a two-dimensional image sensor such as aCCD and a CMOS (complementary metal oxide semiconductor). The imagesensor 422 a may be connected to the shooting controller 81 via theimage measurement control circuit 83. “Image sensor exposure signal”outputted from the image measurement control circuit 83 may be inputtedto the image sensor 422 a. The image sensor exposure signal outputtedfrom the image measurement control circuit 83 may be a control signalfor controlling the operation of the image sensor 422 a to expose thelight receiving surface of the image sensor 422 a to the light. When theinput of the image sensor exposure signal to the image sensor 422 a isstarted, the exposure of the image sensor 422 a may be started. Then,when the input of the image sensor exposure signal is stopped, theexposure of the image sensor 422 a may be stopped. The image sensor 422a after the completion of the exposure may generate the image data ofthe captured image, and output the data to the shooting controller 81.Here, the period of time from when the exposure of the image sensor 422a is started until the exposure is stopped may be referred to as“exposure time Tr.”

The other configuration of the image sensor 422 a may be the same as theconfiguration of the image sensor 422 a shown in FIG. 3. Moreover, theconfigurations of the transfer optical system 422 b and the window 422 cmay be the same as those of the transfer optical system 422 b and thewindow 422 c shown in FIG. 3.

The shutter 422 d may be provided on the light receiving surface of theimage sensor 422 a. The shutter 422 d may be, for example, an imageintensifier with a microchannel plate. Here, the specific configurationof the shutter 422 d will be described in detail later with reference toFIG. 43.

The shutter 422 d may be connected to the shooting controller 81 via theimage measurement control circuit 83. “Shutter opening signal” outputtedfrom the image measurement control circuit 83 may be inputted to theshutter 422 d. The shutter opening signal outputted from the imagemeasurement control circuit 83 may be a control signal for controllingthe opening and closing of the shutter 422 d. When the input of theshutter opening signal to the shutter 422 d is started, the shutter 422d may open. Then, when the input of the shutter opening signal to theshutter 422 d is stopped, the shutter 422 d may close. The image sensor422 a may capture the image formed by the transfer optical system 422 bfrom when the shutter 422 d opens until the shutter 422 d closes. Here,the period of time from when the shutter 422 d opens until the shutter422 d closes may be referred to as “shutter opening time Tex.”

The image measurement control circuit 83 shown in FIG. 5 may be acircuit for controlling the operation timing of the image measurementunit 42. The image measurement control circuit 83 may be providedbetween the shooting controller 81 and the image measurement unit 42.The image measurement control circuit 83 may include an AND circuit 831,an AND circuit 832, a delay circuit 833, a delay circuit 834, a one-shotcircuit 835, and a one-shot circuit 836.

The input side of the AND circuit 831 may be connected to the shootingcontroller 81. The output side of the AND circuit 831 may be connectedto the delay circuit 833 and the delay circuit 834. The dropletdetection signal and “image measurement signal” outputted from theshooting controller 81 may be inputted to the AND circuit 831. Thedroplet detection signal outputted from the shooting controller 81 maybe a signal which has been outputted from the droplet detector 41 and isinputted directly to the AND circuit 831 via the shooting controller 81.The droplet detection signal may be inputted to the AND circuit 831 forthe same cycle as the generation cycle of the droplet 271. The imagemeasurement signal outputted from the shooting controller 81 may be acontrol signal to allow the image measurement unit 42 to perform imagemeasurement. The image measurement signal may have a pulse width longerthan the pulse width of the droplet detection signal and shorter thanthe generation cycle of the droplet 271. When the AND circuit 831receives the droplet detection signal while receiving the imagemeasurement signal, the AND circuit 831 may output enable signals toactivate the delay circuit 833 and the delay circuit 834.

The delay circuit 833 may change the delay time for an input signal,based on the setting by the shooting controller 81. The input side ofthe delay circuit 833 may be connected to the AND circuit 831. Theoutput side of the delay circuit 833 may be connected to the one-shotcircuit 835. Moreover, the input side (not shown) of the delay circuit833 for setting the delay time may be connected to the shootingcontroller 81.

The enable signal outputted from the AND circuit 831 may be inputted tothe delay circuit 833. The delay circuit 833 may output the enablesignal to activate the one-shot circuit 835 at the timing delayed fromthe inputted enable signal by “delay time Tds”. The delay time Tds maybe applied to determine the timing at which the image measurement unit42 starts image measurement. To be more specific, the delay time Tds maybe applied to determine the timing at which the image measurementcontrol circuit 83 outputs a lighting signal to the light source 421 aof the light source part 421. Moreover, the delay time Tds may beapplied to determine the timing at which the image measurement controlcircuit 83 outputs a shutter opening signal to the shutter 422 d of theimaging part 422.

The delay circuit 834 may change the delay time for an input signal,based on the setting by the shooting controller 81. The input side ofthe delay circuit 834 may be connected to the AND circuit 831. Theoutput side of the delay circuit 834 may be connected to the one-shotcircuit 836. Moreover, the input side (not shown) of the delay circuit834 for setting the delay time may be connected to the shootingcontroller 81.

The enable signal outputted from the AND circuit 831 may be inputted tothe delay circuit 834. The delay circuit 834 may output the enablesignal to activate the one-shot circuit 836 at the timing delayed fromthe inputted enable signal by “delay time Tdi.” The delay time Tdi maybe applied to determine the timing at which an image sensor exposuresignal is outputted to the image sensor 422 a of the imaging part 422.The delay time Tdi may be equal to or shorter than the delay time Tds.

The one-shot circuit 835 may change the pulse width of the outputsignal, based on the setting by the shooting controller 81. The pulsewidth which is set in the one-shot circuit 835 by the shootingcontroller 81 may correspond to the above-described shutter opening timeTex. The input side of the one-shot circuit 835 may be connected to thedelay circuit 833. The output side of the one-shot circuit 835 may beconnected to the shutter 422 d of the imaging part 422 and the ANDcircuit 832. Moreover, the input side (not shown) of the one-shotcircuit 835 for setting the pulse width of the output signal may beconnected to the shooting controller 81.

The enable signal outputted from the delay circuit 833 may be inputtedto the one-shot circuit 835. The one-shot circuit 835 may output anoutput signal having the pulse width of the shutter opening time Tex,according to the inputted enable signal as a trigger. According to theoutput signal from the one-shot circuit 835, it is possible to determinethe length of the shutter opening time of the shutter 422 d and thelength of the lighting time of the light source 421 a. Among the outputsignals from the one-shot circuit 835, the signal inputted to theshutter 422 d may function as the above-described shutter openingsignal.

The one-shot circuit 836 may change the pulse width of the outputsignal, based on the setting by the shooting controller 81. The pulsewidth which is set in the one-shot circuit 836 by the shootingcontroller 81 may correspond to the above-described exposure time Tr.The input side of the one-shot circuit 836 may be connected to the delaycircuit 834. The output side of the one-shot circuit 836 may beconnected to the image sensor 422 a of the imaging part 422. Moreover,the input side (not shown) of the one-shot circuit 836 for setting thepulse width of the output signal may be connected to the shootingcontroller 81.

The enable signal outputted from the delay circuit 834 may be inputtedto the one-shot circuit 836. The one-shot circuit 836 may output anoutput signal having the pulse width of the exposure time Tr, accordingto the inputted enable signal as a trigger. According to the outputsignal from the one-shot circuit 836, it is possible to determine thelength of the exposure time Tr of the image sensor 422 a. The outputsignal from the one-shot circuit 836 may be inputted to the image sensor422 a and function as the above-described image sensor exposure signal.

The input side of the AND circuit 832 may be connected to the shootingcontroller 81 and the one-shot circuit 835. The output side of the ANDcircuit 832 may be connected to the light source 421 a of the lightsource part 421. “Gate signal” outputted from the shooting controller 81and the output signal from the one-shot circuit 835 may be inputted tothe AND circuit 832. The gate signal outputted from the shootingcontroller 81 may determine whether or not to turn on the light source421 a. When the AND circuit 832 receives the output signal from theone-shot circuit 835 while receiving the gate signal, the AND circuit832 may output a lighting signal having the same pulse width as thepulse width of the output signal from the one-shot circuit 835, to thelight source 421 a. Here, an instance where the shooting controller 81outputs a gate signal to the AND circuit 832 may be referred to as “gatesignal is turned on.” Meanwhile, an instance where the shootingcontroller 81 does not output a gate signal to the AND circuit 832 maybe referred to as “gate signal is turned off.”

With the above-described configuration, the image measurement controlcircuit 83 can control the operation timing of each component of theimage measurement unit 42, based on various times and various signalsset by the shooting controller 81. In particular, the image measurementcontrol circuit 83 can output the shutter opening signal according tothe delay time Tds and the droplet detection signal, and thereforecontrol the timing at which the imaging part 422 captures the image ofthe imaging region 25 a. Here, the timing at which the imaging part 422captures the image of the imaging region 25 a may be referred to as“imaging timing.” Specifically, the imaging timing may be a timing atwhich the shutter opening signal is outputted, and may be determineddepending on the length of the delay time Tds.

The configuration of the shooting controller 81 shown in FIG. 5 may bethe same as that of the shooting controller 81 shown in FIG. 3, with theexception of the configuration for communication with the imagemeasurement control circuit 83. The configuration of the delay circuit82 shown in FIG. 5 may be the same as that of the delay circuit 82 shownin FIG. 3.

5.2 Operation

With reference to FIGS. 6 to 12, the operation of the image measurementsystem included in the EUV light generation apparatus 1 according toEmbodiment 1 will be described. The operation of the image measurementsystem included in the EUV light generation apparatus 1 according toEmbodiment 1, which is the same as the operation of the EUV lightgeneration apparatus 1 shown in FIGS. 2 and 3, will not be describedagain here. First, with reference to FIGS. 6 and 7, the timing controlfor the image measurement performed by the controller 8 of the EUV lightgeneration apparatus 1 according to Embodiment 1 will be described.

FIG. 6 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 5, where the image of the droplet 271reaching the plasma generation region 25 is measured.

With the time chart shown in FIG. 6, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texa in the one-shot circuit 835 inadvance. The shutter opening time Texa may be a period of time which isnecessary and sufficient to capture the image of the droplet 271. Theshutter opening time Texa may be, for example, 50 ns to 500 ns.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsa in the delay circuit 833. When the image of the droplet 271reaching the plasma generation region 25 is captured, the imaging timingof the imaging part 422 may be set to a timing just before theirradiation timing of the pulsed laser beam 33. That is, a summed value“Tdsa+Texa” of the delay time Tdsa that defines the output timing of theshutter opening signal and the shutter opening time Texa may be equal toor smaller than “delay time Tdl+time α” that defines the irradiationtiming of the pulsed laser beam 33. The delay time Tdsa may becalculated according to the following equation.Tdsa=(d/v)−Texa

Here, d may represent the distance between the plasma generation region25 and the predetermined position P. For example, d may be 1 mm to 2 mm.v may represent the traveling speed of the droplet 271 shown in FIG. 5.For example, v may be 30 m/s to 150 m/s. d/v may be a period of timerequired from when the droplet 271 passes through the predeterminedposition P until reaching the plasma generation region 25.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup.

The droplet 271 may be outputted into the chamber 2 for thepredetermined generation cycle and passthrough the predeterminedposition P on the target traveling path 272. At this time, thecontroller 8 may control the output timings of various signals for theimage measurement as follows, according to the droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 6, the shooting controller 81 may output dropletdetection signals directly to the delay circuit 82 and the AND circuit831.

Then, as shown in FIG. 6, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831 when the shooting controller81 causes the image measurement unit 42 to perform the imagemeasurement.

Then, as shown in FIG. 6, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 833, the delay circuit 833 may outputthe enable signal to the one-shot circuit 835 at the timing delayed bythe delay time Tdsa. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 834, the delay circuit 834 may outputthe enable signal to the one-shot circuit 836 at the timing delayed bythe delay time Tdi.

Then, as shown in FIG. 6, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output an imagesensor exposure signal having the pulse width of the exposure time Tr tothe image sensor 422 a. The image sensor 422 a may be exposed to thelight from when the image sensor exposure signal is inputted to theimage sensor 422 a until the exposure time Tr has elapsed.

Then, as shown in FIG. 6, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the laser device 3 at the timing delayed by the delay timeTdl. After a time α has elapsed from when the trigger signal is inputtedto the laser device 3, the laser device 3 may emit the pulsed laser beam33 to the plasma generation region 25.

Then, as shown in FIG. 6, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texa tothe shutter 422 d and the AND circuit 832. Among the output signals fromthe one-shot circuit 835, the signal inputted to the shutter 422 d mayfunction as a shutter opening signal. The shutter 422 d may be open fromwhen the shutter opening signal is inputted until the shutter openingtime Texa has elapsed.

Then, as shown in FIG. 6, when the output signal from the one-shotcircuit 835 and the gate signal are inputted to the AND circuit 832, theAND circuit 832 may output a lighting signal having the pulse width ofthe shutter opening time Texa to the light source 421 a. The gate signalmay be outputted from the shooting controller 81 to the AND circuit 832before the one-shot circuit 835 outputs the output signal to the ANDcircuit 832. The shooting controller 81 may output the gate signal tothe AND circuit 832 at the same timing as the timing at which theshooting controller 81 outputs the image measurement signal to the ANDcircuit 831. The light source 421 a may emit pulsed light from when thelighting signal is inputted until the shutter opening time Texa haselapsed.

Then, as shown in FIG. 6, plasma light may be emitted after the shutteropening time Texa has elapsed. The imaging part 422 may capture theimage of the droplet 271 just before being irradiated with the pulsedlaser beam 33 in the plasma generation region 25.

Then, as shown in FIG. 6, the image sensor 422 a may generate image dataand output the data to the shooting controller 81 after the exposuretime Tr has elapsed. The shooting controller 81 may acquire the imagedata of the droplet 271 just before being irradiated with the pulsedlaser beam 33 in the plasma generation region 25. The shootingcontroller 81 may measure the state of the droplet 271, based on theacquired image data.

FIG. 7 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 5, where the image of the plasma lightemitted in the plasma generation region 25 is measured.

With the time chart shown in FIG. 7, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texb in the one-shot circuit 835 inadvance. The shutter opening time Texb may be a period of time which isnecessary and sufficient to capture the image of the plasma light. Theshutter opening time Texb may be, for example, 2 ns to 50 ns.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsb in the delay circuit 833. When the image of the plasma lightemitted in the plasma generation region 25 is captured, the imagingtiming of the imaging part 422 may be set to a timing just after theirradiation timing of the pulsed laser beam 33. That is, the delay timeTdsb that defines the output timing of the shutter opening signal may beequal to or greater than “delay time Tdl+time α” that defines theirradiation timing of the pulsed laser beam 33. The delay time Tdsb maybe calculated according to the following equation.Tdsb=d/v

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIG. 6.

In FIG. 7, the controller 8 may control the output timings of varioussignals for the image measurement as follows in the same way as the casein FIG. 6.

As shown in FIG. 7, the shooting controller 81 may output dropletdetection signals directly to the delay circuit 82 and the AND circuit831.

Then, as shown in FIG. 7, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831 when the shooting controller81 causes the image measurement unit 42 to perform the imagemeasurement.

Then, as shown in FIG. 7, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 833, the delay circuit 833 may outputthe enable signal to the one-shot circuit 835 at the timing delayed bythe delay time Tdsb. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 834, the delay circuit 834 may outputthe enable signal to the one-shot circuit 836 at the timing delayed bythe delay time Tdi.

Then, as shown in FIG. 7, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output an imagesensor exposure signal having the pulse width of the exposure time Tr tothe image sensor 422 a. The image sensor 422 a may be exposed to thelight from when the image sensor exposure signal is inputted to theimage sensor 422 a until the exposure time Tr has elapsed.

Then, as shown in FIG. 7, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the laser device 3 at the timing delayed by the delay timeTdl. After the time α has elapsed from when the trigger signal isinputted to the laser device 3, the laser device 3 may emit the pulsedlaser beam 33 to the plasma generation region 25.

Then, as shown in FIG. 7, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texb tothe shutter 422 d and the AND circuit 832. Among the output signals fromthe one-shot circuit 835, the signal inputted to the shutter 422 d mayfunction as a shutter opening signal. The shutter opening signal may beinputted to the shutter 422 d in synchronization with the irradiationtiming of the pulsed laser beam 33. The shutter 422 d may be open fromwhen the shutter opening signal is inputted until the shutter openingtime Texb has elapsed.

Then, as shown in FIG. 7, the AND circuit 832 may not output a lightingsignal to the light source 421 a. When the output signal from theone-shot circuit 835 and the gate signal are inputted to the AND circuit832, the AND circuit 832 may output a lighting signal having the pulsewidth of the shutter opening time Texb to the light source 421 a.However, when the image of the plasma light is captured, the shootingcontroller 81 may not output the gate signal. The reason for this isthat the optical intensity of the plasma light is sufficiently higherthan the optical intensity of the pulsed light emitted from the lightsource 421 a, and therefore it may not necessary to turn on the lightsource 421 a. In addition, when the light source 421 a is not turned on,the light source 421 a does not emit pulsed light interfering with theplasma light, and therefore it is possible to precisely measure thestate of the plasma light. Moreover, if the light source 421 a is notturned on, it is possible to reduce the power consumption.

Then, as shown in FIG. 7, the plasma light may be emitted during theshutter opening time Texb. The imaging part 422 may capture the image ofthe plasma light emitted from the droplet 271 just after beingirradiated with the pulsed laser beam 33 in the plasma generation region25.

Then, as shown in FIG. 7, after the exposure time Tr has elapsed, theimage sensor 422 a may generate image data and output the data to theshooting controller 81. The shooting controller 81 may acquire the imagedata of the plasma light emitted from the droplet 271 just after beingirradiated with the pulsed laser beam 33 in the plasma generation region25. The shooting controller 81 may measure the state of the plasmalight, based on the acquired image data.

Next, with reference to FIGS. 8 to 12, the flow of the process for theimage measurement performed by the shooting controller 81 of the EUVlight generation apparatus 1 according to Embodiment 1 will bedescribed. FIG. 8 is a flowchart showing a process for the imagemeasurement performed by the shooting controller 81.

In step S11, the shooting controller 81 may prepare to output thedroplet 271 into the chamber 2. Upon receiving a target generationsignal from the EUV light generation controller 5, the shootingcontroller 81 may perform the same steps as the steps S2 to S4 shown inFIG. 4, as the preparation for outputting the droplet 271.

In step S12, the shooting controller 81 may set the delay time Tdl forthe trigger signal in the delay circuit 82.

In step S13, the shooting controller 81 may determine whether or not thedroplet 271 is being outputted. The shooting controller 81 may make thedetermination by checking if the droplet detection signal has beeninputted. When determining that the droplet 271 is not being outputted,the shooting controller 81 may wait. On the other hand, when determiningthat the droplet 271 is being outputted, the shooting controller 81 maymove the step to step S14.

In the step S14, the shooting controller 81 may measure the image of thedroplet 271 just before being irradiated with the pulsed laser beam 33.Here, a process for measuring the image of the droplet 271 will bedescribed later with reference to FIG. 9.

In step S15, the shooting controller 81 may determine whether or not thepulsed laser beam 33 is being outputted. The shooting controller 81 maymake the determination by checking if the trigger signal has beeninputted to the laser device 3. When determining that the pulsed laserbeam 33 is not being outputted, the shooting controller 81 may move thestep to the step S13. On the other hand, when determining that thepulsed laser beam 33 is being outputted, the shooting controller 81 maymove the step to step S16.

In the step S16, the shooting controller 81 may measure the image of theplasma light emitted from the droplet 271 just after being irradiatedwith the pulsed laser beam 33. Here, a process for measuring the imageof the plasma light will be described later with reference to FIG. 11.

In step S17, the shooting controller 81 may determine whether or not tostop the process for the image measurement. When determining not to stopthe process for the image measurement, the image shooting controller 81may move the step to the step S13. On the other hand, when determiningto stop the process for the image measurement, the shooting controller81 may end this process.

FIG. 9 is a flowchart showing the process for measuring the image of thedroplet 271 in the step S14 shown in FIG. 8.

In step S141, the shooting controller 81 may set the delay time Tds inthe delay circuit 833. The shooting controller 81 may set the delay timeTds as Tds=Tdsa in order to set the imaging timing of the imaging part422 to a timing just before the irradiation timing of the pulsed laserbeam 33.

In step S142, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texa in order to secure necessaryand sufficient time for which the image sensor 422 a captures the imageof the droplet 271.

In step S143, the shooting controller 81 may output a gate signal to theAND circuit 832, that is, a gate signal may be turned on. The lightsource 421 a may emit pulsed light in synchronization with the imagingtiming.

In step S144, the shooting controller 81 may output an image measurementsignal to the AND circuit 831. The image measurement unit 42 may capturethe image of the imaging region 25 a. The captured image may contain theimage of the droplet 271 just before being irradiated with the pulsedlaser beam 33 in the plasma generation region 25. The image measurementunit 42 may generate image data of the captured image, and output thedata to the shooting controller 81.

In step S145, the shooting controller 81 may determine whether or notthe image data can be acquired. When determining that the image datacannot be acquired because the image measurement unit 42 is not ready tooutput the image data, the shooting controller 81 may wait. On the otherhand, when determining that the image data can be acquired because theimage measurement unit 42 is ready to output the image data, theshooting controller 81 may move the step to step S146.

In the step S146, the shooting controller 81 may acquire the image dataoutputted from the image measurement unit 42.

In step S147, the shooting controller 81 may calculate the parametersfor the state of the droplet 271 just before being irradiated with thepulsed laser beam 33, based on the acquired image data. Here, a processfor calculating the parameters of the droplet 271 will be describedlater with reference to FIG. 10A.

FIG. 10A is a flowchart showing the process for calculating theparameters of the droplet 271 in the step S147 shown in FIG. 9. FIG. 10Bis a drawing showing the image of the droplet 271 captured by theimaging part 422 of the image measurement unit 42.

In step S1471, the shooting controller 81 may calculate a diameter Dd ofthe droplet 271, based on the image of the droplet 271 contained in theimage data acquired in the step S146 shown in FIG. 9.

In step S1472, the shooting controller 81 may calculate a position Cd ofthe droplet 271, based on the image of the droplet 271 contained in theacquired image data.

The image of the droplet 271 captured by one imaging operation of theimaging part 422 may be an image illustrated in FIG. 10B. The shootingcontroller 81 may calculate the diameter Dd and the position Cd of thedroplet 271 by the following way.

The shooting controller 81 may regard the width of the image of thedroplet 271 in the Y direction that is the traveling direction of thedroplet 271 as the diameter Dd. When the shadow of the approximatelyspherical droplet 271 is captured as one image having an approximatelyspherical shape, the shooting controller 81 may regard the average ofthe width of the droplet 271 in the Y direction and the width of thedroplet 271 in the Z direction perpendicular to the Y direction, as thediameter Dd of the droplet 271.

In addition, the shooting controller 81 may regard the center positionof the image of the droplet 271 as the position Cd of the droplet 271.To be more specific, the shooting controller 81 may regard a specificpoint in the imaging region 25 a as the original point. Then, theshooting controller 81 may calculate the distance from the originalpoint to the center of the image of the droplet 271 in the Y direction.At the same time, the shooting controller 81 may calculate the distancefrom the original point to the center of the image of the droplet 271 inthe Z direction. Then, the shooting controller 81 may regard thecalculated distances in the Y direction and the Z direction ascoordinate values of the position Cd(y, z) of the droplet 271.

FIG. 11 is a flowchart showing the process for measuring the image ofthe plasma light in the step S16 shown in FIG. 8.

In step S161, the shooting controller 81 may set the delay time Tds inthe delay circuit 833. The shooting controller 81 may set the delay timeTds as Tds=Tdsb in order to set the imaging timing of the imaging part422 to a timing just after the irradiation timing of the pulsed laserbeam 33.

In step S162, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texb in order to secure necessaryand sufficient time for which the image sensor 422 a captures the imageof the plasma light.

In step S163, the shooting controller 81 may not output a gate signal tothe AND circuit 832, that is, a gate signal may be turned off. By thismeans, the light source 421 a may not emit pulsed light.

In step S164, the shooting controller 81 may output an image measurementsignal to the AND circuit 831. The image measurement unit 42 may capturethe image of the imaging region 25 a. The captured image may contain theimage of the plasma light emitted from the droplet 271 just after beingirradiated with the pulsed laser beam 33 in the plasma generation region25. The image measurement unit 42 may generate image data of thecaptured image, and output the data to the shooting controller 81.

In step S165, the shooting controller 81 may determine whether or notthe image data can be acquired. When determining that the image datacannot be acquired because the image measurement unit 42 is not ready tooutput the image data, the shooting controller 81 may wait. On the otherhand, when determining that the image data can be acquired because theimage measurement unit 42 is ready to output the image data, theshooting controller may move the step to step S166.

In the step S166, the shooting controller 81 may acquire the image dataoutputted from the image measurement unit 42.

In step S167, the shooting controller 81 may calculate the parametersfor the state of the plasma light emitted from the droplet 271 justafter being irradiated with the pulsed laser beam 33, based on theacquired image. Here, a process for calculating the parameters of theplasma light will be described later with reference to FIG. 12A.

FIG. 12A is a flowchart showing the process for calculating theparameters of the plasma light in the step S167 shown in FIG. 11. FIG.12B is a drawing showing the image of the plasma light captured by theimaging part 422 of the image measurement unit 42.

In step S1671, the shooting controller 81 may calculate a diameter Dp ofthe plasma light, based on the image of the plasma light contained inthe image data acquired in the step S166 shown in FIG. 11.

In step S1672, the shooting controller 81 may calculate a position Cp ofthe plasma light, based on the image of the plasma light contained inthe acquired image data.

The image of the plasma light captured by one imaging operation of theimaging part 422 may be an image illustrated in FIG. 12B. The shootingcontroller 81 may calculate the diameter Dp and the position Cp of theplasma light by the following way.

The shooting controller 81 may regard the width of the image of theplasma light in the Y direction which is the traveling direction of thedroplet 271, as the diameter Dp of the plasma light. When the image ofthe plasma light is captured as one approximately oval sphere, theshooting controller 81 may regard the width of the longer diameter asthe diameter Dp of the plasma light. The shooting controller 81 may findthe spatial and spectral distribution of the optical intensity of theplasma light, and regard (1/e)² width of the distribution as thediameter Dp of the plasma light.

In addition, the shooting controller 81 may regard the center positionof the image of the plasma light as the position Cp of the plasma light.To be more specific, the shooting controller 81 may regard a specificpoint in the imaging region 25 a as the original point. Then, theshooting controller 81 may calculate the distance from the originalpoint to the center of the image of the plasma light in the Y direction.At the same time, the shooting controller 81 may calculate the distancefrom the original point to the center of the image of the plasma lightin the Z direction. Then, the shooting controller 81 may regard thecalculated distances in the Y direction and the Z direction as thecoordinate values of the position Cp(y, z) of the plasma light. Theshooting controller 81 may find the spatial distribution of the opticalintensity of the plasma light, and regard the position corresponding tothe weighted average efficiency of the optical intensity as the positionCp of the plasma light.

5.3 Effect

The EUV light generation apparatus 1 according to Embodiment 1 maycapture the image of the droplet 271 just before being irradiated withthe pulsed laser beam 33 in the plasma generation region 25. The EUVlight generation apparatus 1 may calculate the parameters of the droplet271 based on the captured image. Therefore, the EUV light generationapparatus 1 can precisely measure the state of the droplet 271 justbefore being irradiated with the pulsed laser beam 33 in the plasmageneration region 25. Then, the EUV light generation apparatus 1 cancorrectly recognize whether or not the droplet 271 is in the certainstate by comparing the calculated value with the target value of theparameter.

The EUV light generation apparatus 1 according to Embodiment 1 maycapture the image of the plasma light emitted from the droplet 271 justafter being irradiated with the pulsed laser beam 33 in the plasmageneration region 25. The EUV light generation apparatus 1 may calculatethe parameters of the plasma light based on the captured image.Therefore, the EUV light generation apparatus 1 can precisely measurethe state of the plasma light emitted from the droplet 271 just afterbeing irradiated with the pulsed laser beam 33 in the plasma generationregion 25. Then, the EUV light generation apparatus 1 can correctlyrecognize whether or not the plasma light is in the certain state bycomparing the calculated value with the target value of the parameter.

Then, with the EUV light generation apparatus 1 according to Embodiment1, the controller 8 controls the timings of the image measurement, andtherefore it is possible to capture both the image of the droplet 271and the image of the plasma light in the plasma generation region 25 bythe single imaging part 422.

6. Shooting System Using the EUV Light Generation Apparatus According toEmbodiment 2

6.1 Configuration

The shooting system using the EUV light generation apparatus 1 accordingto Embodiment 2 may further include the laser device 3, a laser lightfocusing optical system 22 a, a triaxial stage 226 and an imagemeasurement unit 43, in addition to the components included in the imagemeasurement system of the EUV light generation apparatus 1 according toEmbodiment 1. This shooting system may measure the states of the droplet271 and the plasma light in the plasma generation region 25. Moreover,the shooting system may control the position of the droplet 271, theposition of the plasma light, and the focused position of the pulsedlaser beam 33 in the plasma generation region 25.

Now, the configuration of the shooting system using the EUV lightgeneration apparatus 1 according to Embodiment 2 will be described withreference to FIG. 13. In FIG. 13, an H-axis may be a coordinate axis inan X-Y plane and have an angle of 45 degrees with respect to the X-axis.An L-axis may be a coordinate axis in the X-Y plane and be orthogonal tothe H-axis.

The shooting system using the EUV light generation apparatus 1 accordingto Embodiment 2 may include the laser device 3, the laser beam focusingoptical system 22 a, the triaxial stage 226, the target generator 7, thedroplet detector 41, the image measurement unit 42, the imagemeasurement unit 43, and the controller 8. The controller 8 may includethe shooting controller 81, the delay circuit 82, and the imagemeasurement control circuit 83. The configurations of the shootingsystem shown in FIG. 13, which are the same as those of the EUV lightgeneration apparatus 1 and the image measurement system shown in FIGS. 1to 3 and 5, will not be described again here.

The configuration of the laser device 3 shown in FIG. 13 may be the sameas that of the laser device 3 shown in FIG. 2. The configuration of thelaser beam focusing optical system 22 a shown in FIG. 13 may be the sameas that of the laser beam focusing optical system 22 a shown in FIG. 2.The configuration of the triaxial stage 226 shown in FIG. 13 may be thesame as that of the triaxial stage 226 shown in FIG. 2. Theconfiguration of the target generator 7 shown in FIG. 13 may be the sameas that of the target generator 7 shown in FIG. 5. The configuration ofthe droplet detector 41 shown in FIG. 13 may be the same as that of thedroplet detector 41 shown in FIG. 5.

The image measurement unit 42 and the image measurement unit 43 shown inFIG. 13 may measure the images of the droplet 271 and the plasma lightin the plasma generation region 25, in the same way as the imagemeasurement unit 42 shown in FIG. 5. Here, the image data of the imagecaptured by the image measurement unit 42 may be referred to as “imagedata 1”. The image data of the image captured by the image measurementunit 43 may be referred to as “image data 2”.

The image measurement unit 42 shown in FIG. 13 may capture the image ofthe imaging region 25 a in the normal direction of an L-Z plane, andmeasure the images of the droplet 271 and the plasma light. Thedirection in which the light source part 421 faces the imaging part 422of the image measurement unit 42 may be the normal direction of the L-Zplane. The other configuration of the image measurement unit 42 may bethe same as that of the image measurement unit 42 shown in FIG. 5.

The image measurement unit 43 shown in FIG. 13 may capture the image ofthe imaging region 25 a in the normal direction of an H-Z plane, andmeasure the images of the droplet 271 and the plasma light. The imagemeasurement unit 43 may include a light source part 431 and an imagingpart 432. The light source part 431 and the imaging part 432 may bearranged to face one another across the plasma generation region 25 onthe target traveling path 272. The direction in which the light sourcepart 431 faces the imaging part 432 may be the normal direction of theH-Z plane.

The light source part 431 may include a light source 431 a, anillumination optical system 431 b and a window 431 c. The light source431 a may be connected to the shooting controller 81 via the imagemeasurement control circuit 83. A lighting signal outputted from theimage measurement control circuit 83 may be inputted to the light source431 a. The light source 431 a may emit pulsed light according to thelighting signal outputted from the image measurement control circuit 83.The other configuration of the light source 431 a may be the same asthat of the light source 421 a shown in FIG. 5. In addition, theconfigurations of the illumination optical system 431 b and the window431 c may be the same as those of the illumination optical system 421 band the window 421 c shown in FIG. 5.

The imaging part 432 may capture the image of the imaging region 25 a(not shown in FIG. 13) in the same way as the imaging part 422 shown inFIG. 5. The imaging part 432 may include an image sensor 432 a, atransfer optical system 432 b, a window 432 c and a shutter 432 d.

The image sensor 432 a may be connected to the shooting controller 81via the image measurement control circuit 83. An image sensor exposuresignal outputted from the image measurement control circuit 83 may beinputted to the image sensor 432 a. When the input of the image sensorexposure signal to the image sensor 432 a is started, the exposure ofthe image sensor 432 a may be started. Then, when the input of the imagesensor exposure signal to the image sensor 432 a is stopped, theexposure of the image sensor 432 a may be stopped. The image sensor 432a may be connected to the shooting controller 81. The image sensor 432 amay output the image data 2 of the captured image to the shootingcontroller 81. The other configuration of the image sensor 432 a may bethe same as that of the image sensor 422 a shown in FIG. 5.

The shutter 432 d may be connected to the shooting controller 81 via theimage measurement control circuit 83. A shutter opening signal outputtedfrom the image measurement control circuit 83 may be inputted to theshutter 432 d. When the input of the shutter opening signal to theshutter 432 d is started, the shutter 432 d may open. Then, when theinput of the shutter opening signal to the shutter 432 d is stopped, theshutter 432 d may close. The other configuration of the shutter 432 dmay be the same as that of the shutter 422 d shown in FIG. 5. Moreover,the configurations of the transfer optical system 432 b and the window432 c may be the same as those of the transfer optical system 422 b andthe window 422 c shown in FIG. 5.

The image measurement control circuit 83 shown in FIG. 13 may controlthe operation timings of the image measurement unit 42 and the imagemeasurement unit 43. The image measurement control circuit 83 may beprovided between the shooting controller 81 and the image measurementunits 42 and 43. The image measurement control circuit 83 may includethe AND circuit 831, the AND circuit 832, the delay circuit 833, thedelay circuit 834, the one-shot circuit 835, and the one-shot circuit836.

The configurations of the AND circuit 831, the delay circuit 833, andthe delay circuit 834 may be the same as those of the AND circuit 831,the delay circuit 833, and the delay circuit 834 shown in FIG. 5.

The output side of the one-shot circuit 835 may be connected to theshutter 422 d of the imaging part 422, the shutter 432 d of the imagingpart 432, and the AND circuit 832. The output signals from the one-shotcircuit 835 may be inputted to the shutter 422 d and the shutter 432 dat the same timing, as the shutter opening signals. The otherconfiguration of the one-shot circuit 835 may be the same as that of theone-shot circuit 835 shown in FIG. 5.

The output side of the one-shot circuit 836 may be connected to theimage sensor 422 a of the imaging part 422 and the image sensor 432 a ofthe imaging part 432. The output signals from the one-shot circuit 836may be inputted to the image sensor 422 a and the image sensor 432 a atthe same timing, as the image sensor exposure signals. The otherconfiguration of the one-shot circuit 836 may be the same as that of theone-shot circuit 836 shown in FIG. 5.

The output side of the AND circuit 832 may be connected to the lightsource 421 a of the light source part 421 and the light source 431 a ofthe light source part 431. The output signals from the AND circuit 832may be inputted to the light source 421 a and the light source 431 a atthe same timing, as the lighting signals. The other configuration of theAND circuit 832 may be the same as that of the AND circuit 832 shown inFIG. 5.

The shooting controller 81 shown in FIG. 13 may acquire the image data 1outputted from the image measurement unit 42. The shooting controller 81may acquire the image data 2 outputted from the image measurement unit43. The shooting controller 81 may calculate the parameters for thestates of the droplet 271 and the plasma light in the plasma generationregion 25, based on the acquired image data 1 and image data 2. Theshooting controller 81 may set the delay time Tds and the delay timeTdl, and control the operation of the biaxial stage 74, based on thecalculation result of the parameters of droplet 271. By this means, theshooting controller 81 can control the position of the droplet 271reaching the plasma generation region 25. The shooting controller 81 maycontrol the operation of the triaxial stage 226, based on thecalculation result of the parameters of the plasma light. By this means,the shooting controller 81 can control the focused position of thepulsed laser beam 33 in the plasma generation region 25. The otherconfiguration of the shooting controller 81 may be the same as that ofthe shooting controller 81 shown in FIG. 5. The configuration of thedelay circuit 82 shown in FIG. 13 may be the same as that of the delaycircuit 82 shown in FIG. 5.

6.2 Operation

Now, the operation of the shooting system using the EUV light generationapparatus 1 according to Embodiment 2 will be described with referenceto FIGS. 14 to 23. The operations of the shooting system using the EUVlight generation apparatus 1 according to Embodiment 2, which are thesame as those of the EUV light generation apparatus 1 shown in FIGS. 2and 3 and the image measurement system according to Embodiment 1, willnot be described again here. FIG. 14 is a flowchart showing a processfor the shooting control performed by the shooting controller 81 shownin FIG. 13.

In step S21, the shooting controller 81 may output an NG signal to theexposure apparatus controller 61 via the EUV light generation controller5. The NG signal may be a signal to report that the EUV light generationapparatus 1 is not ready to output the EUV light 252 generated in anappropriate condition to the exposure apparatus 6.

In step S22, the shooting controller 81 may read a target positionPpt(Xpt, Ypt, Zpt) of the plasma light. The target position Ppt(Xpt,Ypt, Zpt) of the plasma light may be a target value for the centerposition of the plasma light emitted in the plasma generation region 25.In particular, the target position Ppt (Xpt, Ypt, Zpt) of the plasmalight may be a target value for the center position of the plasma lightemitted from the droplet 271 just after being irradiated with the pulsedlaser beam 33 in the plasma generation region 25. The target positionPpt(Xpt, Ypt, Zpt) may be a predetermined value by the EUV lightgeneration controller 5 according to a command from the exposureapparatus controller 61. The shooting controller 81 may read the targetposition Ppt (Xpt, Ypt, Zpt) of the plasma light stored in the EUV lightgeneration controller 5.

In step S23, the shooting controller 81 may calculate a target positionPdt of the droplet 271. The target position Pdt(Xdt, Ydt, Zdt) of thedroplet 271 may be a target value for the center position of the droplet271 reaching the plasma generation region 25. In particular, the targetposition Pdt(Xdt, Ydt, Zdt) of the droplet 271 may be a target value forthe center position of the droplet 271 just before being irradiated withthe pulsed laser beam 33 in the plasma generation region 25. Theshooting controller 81 may calculate the target position Pdt of thedroplet 271 supplied to the plasma generation region 25, based on thetarget position Ppt of the plasma light read in the step S22. Here, aprocess for calculating the target position Pdt of the droplet 271 willbe described later with reference to FIG. 15A.

In step S24, the shooting controller 81 may set the target position Pdtof the droplet 271 and the target focused position of the pulsed laserbeam 33. The shooting controller 81 may set the delay time Tds, thedelay time Tdl and the biaxial stage 74 such that the droplet 271 issupplied to the target position Pdt of the droplet 271 calculated in thestep S23. The shooting controller 81 may set the triaxial stage 226 suchthat the pulsed laser beam 33 is focused on the target position Pdt ofthe droplet 271 calculated in the step S23. Here, a process for settingthe target position Pdt of the droplet 271 and the target focusedposition of the pulsed laser beam 33 will be described later withreference to FIG. 16.

In step S25, the shooting controller 81 may determine whether or not thedroplet 271 is being outputted. The shooting controller 81 may make thedetermination by checking if the droplet detection signal has beeninputted. When determining that the droplet 271 is not being outputted,the shooting controller 81 may wait. On the other hand, when determiningthat the droplet 271 is being outputted, the shooting controller 81 maymove the step to step S26.

In the step S26, the shooting controller 81 may control the position ofthe droplet 271. The shooting controller 81 may cause the imagemeasurement unit 42 and the image measurement unit 43 to measure theimage of the droplet 271 just before being irradiated with the pulsedlaser beam 33 in the plasma generation region 25. Then, the shootingcontroller 81 may calculate a measurement position Cd(Xd, Yd, Zd) of thedroplet 271, based on the acquired image data. Then, the shootingcontroller 81 may appropriately modify and set the delay time Tds andthe delay time Tdl, and control the operation of the biaxial stage 74,based on the calculated measurement position Cd(Xd, Yd, Zd) of thedroplet 271. Here, a process for controlling the position of the droplet271 will be described later with reference to FIG. 17.

The measurement position Cd(Xd, Yd, Zd) of the droplet 271 may be ameasured value for the center position of the droplet 271 reaching theplasma generation region 25. In particular, the measurement positionCd(Xd, Yd, Zd) of the droplet 271 may be a measured value for the centerposition of the droplet 271 just before being irradiated with the pulsedlaser beam 33 in the plasma generation region 25. That is, themeasurement position Cd(Xd, Yd, Zd) of the droplet 271 may berepresented by the coordinates of the center position of the droplet 271which has been actually outputted into the chamber 2 and is reaching theplasma generation region 25.

In step S27, the shooting controller 81 may determine whether or not theposition of the droplet 271 is within an allowable range. The shootingcontroller 81 may determine whether or not the measurement positionCd(Xd, Yd, Zd) of the droplet 271 after the control in the step S26fulfills all the following equations.|Xd−Xdt|≤ΔXdmax|Yd−Ydt|≤ΔYdmax|Zd−Zdt|≤ΔZdmax

Here, ΔXdmax, ΔYdmax and ΔZdmax in the right-hand side may be thethreshold values for the respective coordinates that define theallowable range of the difference in the measurement position Cd fromthe target position Pdt of the droplet 271. ΔXdmax, ΔYdmax and ΔZdmaxmay be predetermined values to efficiently generate plasma light. Whendetermining that the position of the droplet 271 is out of the allowablerange, the shooting controller 81 may move the step to step S25. On theother hand, when determining that the position of the droplet 271 iswithin the allowable range, the shooting controller 81 may move the stepto step S28.

In the step S28, the shooting controller 81 may determine whether or notthe pulsed laser beam 33 is being outputted. The shooting controller 81may make the determination by checking if the trigger signal has beeninputted to the laser device 3. When determining that the pulsed laserbeam 33 is not being outputted, the shooting controller 81 may move thestep to the step S25. On the other hand, when determining that thepulsed laser beam 33 is being outputted, the shooting controller 81 maymove the step to step S29.

In the step S29, the shooting controller 81 may control the focusedposition of the pulsed laser beam 33. The shooting controller 81 maycause the image measurement unit 42 and the image measurement unit 43 tomeasure the image of the plasma light emitted from the droplet 271 justafter being irradiated with the pulsed laser beam 33 in the plasmageneration region 25. Then, the shooting controller 81 may calculate themeasurement position Cp(Xp, Yp, Zp) of the plasma light, based on theacquired image data. Then, the shooting controller 81 may control theoperation of the triaxial stage 226, based on the calculated measurementposition Cp(Xp, Yp, Zp) of the plasma light. Here, a process forcontrolling the focused position of the pulsed laser beam 33 will bedescribed later with reference to FIG. 20.

The measurement position Cp(Xp, Yp, Zp) of the plasma light may be ameasured value for the center position of the plasma light emitted inthe plasma generation region 25. In particular, the measurement positionCp(Xp, Yp, Zp) of the plasma light may be a measured value for thecenter position of the plasma light emitted from the droplet 271 justafter being irradiated with the pulsed laser beam 33 in the plasmageneration region 25. That is, the measurement position Cp(Xp, Yp, Zp)of the plasma light may be represented by the coordinates of the centerposition of the plasma light actually emitted from the droplet 271 byirradiating the droplet 271 with the pulsed laser beam 33 after thedroplet 271 is actually outputted into the chamber 2 and reaches theplasma generation region 25.

In step S30, the shooting controller 81 may determine whether or not theposition of the plasma light is within the allowable range. The shootingcontroller 81 may determine whether or not the measurement positionCp(Xp, Yp, Zp) of the plasma light based on the focused position of thepulsed laser beam 33 after the control in the step S29 fulfills all thefollowing expressions.|Xp−Xpt|≤ΔXpmax|Yp−Ypt|≤ΔYpmax|Zp−Zpt|≤ΔZpmax

Here, ΔXpmax, ΔYpmax and ΔZpmax in the right-hand side may be thethreshold values for the respective coordinates that define theallowable range of the difference in the measurement position Cp fromthe target position Ppt of the plasma light. ΔXpmax, ΔYpmax and ΔZpmaxmay be predetermined values to efficiently generate the plasma light andthe EUV light 252. When determining that the position of the plasmalight is within the allowable range, the shooting controller 81 may movethe step to step S32. On the other hand, when determining that theposition of the plasma light is out of the allowable range, the shootingcontroller 81 may move the step to step S31.

In the step S31, the shooting controller 81 may output an NG signal tothe exposure apparatus controller 61 via the EUV light generationcontroller 5. After outputting the NG signal, the shooting controller 81may move the step to the step S25.

In the step S32, the shooting controller 81 may output an OK signal tothe exposure apparatus controller 61 via the EUV light generationcontroller 5. The OK signal may be a signal to report that the EUV lightgeneration apparatus 1 is ready to output the EUV light 252 generated inan appropriate condition to the exposure apparatus 6.

In step S33, the shooting controller 81 may determine whether or not tostop the process for the shooting control. When determining not to stopthe process for the shooting control, the shooting controller 81 maymove the step to the step S25. On the other hand, when determining tostop the process for the shooting control, the shooting controller 81may end this process.

FIG. 15A is a flowchart showing the process for calculating the targetposition Pdt of the droplet 271 in the step S23 shown in FIG. 14. FIG.15B is a drawing explaining the process shown in FIG. 15A.

In step S231, the shooting controller 81 may calculate the respectivecoordinates of the target position Pdt(Xdt, Ydt, Zdt) of the droplet 271supplied to the plasma generation region 25. The shooting controller 81may calculate the target position Pdt(Xdt, Ydt, Zdt) of the droplet 271according to the following equations, based on the target position Ppt(Xpt, Ypt, Zpt) of the plasma light read in the step S22 shown in FIG.14.Xdt=XptYdt=YptZdt=Zpt+Zdc

That is, the shooting controller 81 may regard the X-component Xpt ofthe target position Ppt of the plasma light as the same as theX-component Xdt of the target position Pdt of the droplet 271. Theshooting controller 81 may regard the Y-component Ypt of the targetposition Ppt of the plasma light as the same as the Y-component Ydt ofthe target position Pdt of the droplet 271. The shooting controller 81may regard the coordinate shifted from the Z-component Zpt of the targetposition Ppt of the plasma light by Zdc in the +Z direction as theZ-component Zdt of the target position Pdt of the droplet 271.

The target position Ppt of the plasma light may be a predetermined valueby the EUV light generation controller 5, according to a command fromthe exposure apparatus controller 61. In order to emit the plasma lightat the target position Ppt of the plasma light, the shooting controller81 may substantially match the target position Pdt of the droplet 271and the target focused position of the pulsed laser beam 33 with thetarget position Ppt of the plasma light. However, if the target positionPdt of the droplet 271 and the target focused position of the pulsedlaser beam 33 are simply matched with the target position Ppt of theplasma light, the following problem may occur. Although the position ofthe plasma light actually emitted in the plasma generation region 25 isnot shifted from the target position Ppt in the X and Y directions, itmay be shifted from the target position Ppt in the Z direction. Thecenter of the plasma light may be located at or near the periphery ofthe droplet 271 in the −Z direction side because the irradiation withthe pulsed laser beam 33 is started at the periphery of the droplet 271in the −Z direction side. Therefore, the center of the plasma light maybe shifted from the center of the droplet 271 in the −Z direction. Bythis means, the position of the plasma light actually emitted in theplasma generation region 25 may be shifted from the target position Ppt.Here, the amount of shifting of the center of the plasma light in the −Zdirection from the center of the droplet 271 is represented as “Zdc.”Therefore, as shown in FIG. 15B, with respect to the Z direction, theshooting controller 81 may set the target position Pdt of the droplet271 and the target focused position of the pulsed laser beam 33 to thecoordinate shifted from the target position Ppt of the plasma light byZdc in the +Z direction.

It is preferred that both the target position Pdt of the droplet 271 andthe focused position of the pulsed laser beam 33 are shifted in the Zdirection rather than only the target position Pdt of the droplet 271 isshifted from the target position Ppt of the plasma light in the Zdirection. The reason for this is that the plasma light can be moreefficiently generated when the focused position of the pulsed laser beam33 is located at the center of the droplet 271 than when the focusedposition of the pulsed laser beam 33 is located at the periphery of thedroplet 271. By this means, the shooting controller 81 can substantiallymatch the position of the plasma light actually emitted in the plasmageneration region 25 with the target position Ppt of the plasma light,and efficiently generate plasma light.

FIG. 16 is a flowchart showing the process for setting the targetposition Pdt of the droplet 271 and the target focused position of thepulsed laser beam 33 in the step S24 shown in FIG. 14.

In step S241, in order to allow the position of the droplet 271 suppliedto the plasma generation region 25 to be the target position Pdt of thedroplet 271, the shooting controller 81 may set the delay time Tds, thedelay time Tdl and the biaxial stage 74 as follows. For the setting inthe X direction and the Z direction, the shooting controller 81 maycontrol the operation of the biaxial stage 74. To be more specific, theshooting controller 81 may set the biaxial stage 74 by controlling thebiaxial stage 74 to be driven by a predetermined amount in the Xdirection and/or the Z direction. The shooting controller 81 may outputa control signal containing the amount of movement of the target supplypart 26 in the X direction and the Z direction, to the biaxial stage 74.For the setting in the Y direction, the shooting controller 81 may setthe delay time Tds and the delay time Tdl. The shooting controller 81may set the delay time Tds in the delay circuit 833 and also set thedelay time Tdl in the delay circuit 82.

In step S242, the shooting controller 81 may set the triaxial stage 226such that the focused position of the pulsed laser beam 33 in the plasmageneration region 25 is the target position Pdt of the droplet 271. Theshooting controller 81 may output a control signal containing the amountof movement of the laser beam focusing optical system 22 a, to thetriaxial stage 226.

FIG. 17 is a flowchart showing the process for controlling the positionof the droplet 271 in the step S26 shown in FIG. 14.

In step S261, the shooting controller 81 may measure the image of thedroplet 271 just before being irradiated with the pulsed laser beam 33.Here, a process for measuring the image of the droplet 271 will bedescribed later with reference to FIG. 18.

In step S262, the shooting controller 81 may calculate the differencebetween the target position Pdt and the measurement position Cd of thedroplet 271 for each of the coordinates. The shooting controller 81 maycalculate, for each of the coordinates, the difference between thetarget position Pdt(Xdt, Ydt, Zdt) set in the step S24 shown in FIG. 14and the measurement position Cd(Xd, Yd, Zd) measured in the step S261,according to the following equations.ΔXd=Xdt−XdΔYd=Ydt−YdΔZd=Zdt−Zd

In step S263, the shooting controller 81 may output a control signal tomove the target supply part 26 in the X direction and the Z direction,to the biaxial stage 74. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the X direction and the Z direction, by controlling the operation ofthe biaxial stage 74. The shooting controller 81 may regard ΔXdcalculated in the step S262 as the amount of the movement of the targetsupply part 26 in the X direction. The shooting controller 81 may regardΔZd calculated in the step S262 as the amount of the movement of thetarget supply part 26 in the Z direction. The shooting controller 81 mayoutput the control signal containing ΔXd and ΔZd to the biaxial stage74.

In step S264, the shooting controller 81 may calculate a time ΔTyrequired to move the droplet 271 by ΔYd. The shooting controller 81 maycalculate ΔTy by using ΔYd calculated in the step S262, according to thefollowing equation.ΔTy=ΔYd/v

Here, v in the right-hand side may be the traveling speed of the droplet271.

In step S265, the shooting controller 81 may modify the delay time Tdsa.The shooting controller 81 may control the position of the droplet 271supplied to the plasma generation region 25 in the Y direction bysetting the delay time Tdsa and the delay time Tdl. The shootingcontroller 81 may calculate the modified delay time Tdsa by using ΔTycalculated in the step S264, according to the following equation.Tdsa=Tdsa+ΔTy

The shooting controller 81 may set the modified delay time Tdsa in thedelay circuit 833.

In step S266, the shooting controller 81 may modify the delay time Tdl.The shooting controller 81 may calculate the modified delay time Tdl byusing ΔTy calculated in the step S264, according to the followingequation.Tdl=Tdl+ΔTy

The shooting controller 81 may set the modified delay time Tdl in thedelay circuit 82.

In step S267, the shooting controller 81 may measure the image of thedroplet 271 just before being irradiated with the pulsed laser beam 33.Here, the process for measuring the image of the droplet 271 will bedescribed later with reference to FIG. 18.

FIG. 18 is a flowchart showing the process for measuring the image ofthe droplet 271 in the step S261 and the step S267 shown in FIG. 17.

In step S2611, the shooting controller 81 may set the delay time Tds inthe delay circuit 833. The shooting controller 81 may set the delay timeTds as Tds=Tdsa in order to set the imaging timing of the imaging part422 and the imaging part 423 to a timing just before the irradiationtiming of the pulsed laser beam 33.

In step S2612, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texa in order to secure necessaryand sufficient time for which the image sensor 422 a and the imagesensor 432 a capture the image of the droplet 271.

In step S2613, the shooting controller 81 may output a gate signal tothe AND circuit 832, that is, the gate signal may be turned on. Thelight source 421 a and the light source 431 a may emit pulsed light insynchronization with the imaging timing.

In step S2614, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831. The image measurement unit 42and the image measurement unit 43 may capture the image of the imagingregion 25 a. The captured image may contain the image of the droplet 271just before being irradiated with the pulsed laser beam 33 in the plasmageneration region 25. The image measurement unit 42 and the imagemeasurement unit 43 may generate image data of the captured image, andoutput the data to the shooting controller 81.

In step S2615, the shooting controller 81 may determine whether or notthe image data 1 and the image data 2 can be acquired. When determiningthat the image data 1 and the image data 2 cannot be acquired becausethe image measurement unit 42 and the image measurement unit 43 are notready to output the image data 1 and the image data 2, the shootingcontroller 81 may wait. On the other hand, when determining that theimage data 1 and the image data 2 can be acquired because the imagemeasurement unit 42 and the image measurement unit 43 are ready tooutput the image data 1 and the image data 2, the shooting controller 81may move the step to step S2616.

In the step S2616, the shooting controller 81 may acquire the image data1 and the image data 2 outputted from the image measurement unit 42 andthe image measurement unit 43.

In step S2617, the shooting controller 81 may calculate the position ofthe droplet 271 just before being irradiated with the pulsed laser beam33, based on the acquired image data 1 and image data 2. Here, a processfor calculating the position of the droplet 271 will be described laterwith reference to FIG. 19.

FIG. 19 is a flowchart showing the process for calculating the positionof the droplet 271 in the step S2617 shown in FIG. 18.

In step S2617-1, the shooting controller 81 may calculate a measurementposition Cd(Ld, Zd) of the droplet 271, based on the image of thedroplet 271 contained in the image data 1 acquired in the step S2616shown in FIG. 18. The image measurement unit 42 may measure the image ofthe droplet 271 in the normal direction of the L-Z plane. The imagecontained in the image data 1 acquired from the image measurement unit42 may be an image of the droplet 271 projected onto the L-Z plane.Therefore, the coordinates of the measurement position Cd of the droplet271, which can be calculated based on the image data 1, may berepresented by an L-component Ld and a Z-component Zd.

In step S2617-2, the shooting controller 81 may calculate a measurementposition Cd(Hd, Zd) of the droplet 271, based on the image of thedroplet 271 contained in the image data 2 acquired in the step S2616 inFIG. 18. The image measurement unit 43 may measure the image of thedroplet 271 in the normal direction of the H-Z plane. The imagecontained in the image data 2 acquired from the image measurement unit43 may be an image of the droplet 271 projected onto the H-Z plane.Therefore, the coordinates of the measurement position Cd of the droplet271, which can be calculated based on the image data 2, may berepresented by an H-component Hd and the Z-component Zd.

In step S2617-3, the shooting controller 81 may calculate themeasurement position Cd(Xd, Yd, Zd) of the droplet 271. The shootingcontroller 81 may calculate the measurement position Cd(Xd, Yd, Zd) ofthe droplet 271, by the coordinate transformation of the Cd(Ld, Zd)calculated in the step S2617-1 and the Cd(Hd, Zd) calculated in the stepS2617-2.

FIG. 20 is a flowchart showing the process for controlling the focusedposition of the pulsed laser beam 33 in the step S29 shown in FIG. 14.

In step S291, the shooting controller 81 may measure the image of theplasma light just after being irradiated with the pulsed laser beam 33.Here, a process for measuring the image of the plasma light will bedescribed later with reference to FIG. 21.

In step S292, the shooting controller 81 may calculate the differencebetween the target position Ppt and the measurement position Cp of theplasma light, by using each of the coordinates. The shooting controller81 may calculate, for each of the coordinates, the difference betweenthe target position Ppt(Xpt, Ypt, Zpt) read in the step S22 shown inFIG. 14 and the measurement position Cp(Xp, Yp, Zp) measured in the stepS291, according to the following equations.ΔXp=Xpt−XpΔYp=Ypt−YpΔZp=Zpt−Zp

In step S293, the shooting controller 81 may output a control signal tomove the laser beam focusing optical system 22 a in the X direction andthe Y direction, to the triaxial stage 226. The shooting controller 81may control the focused position of the pulsed laser beam 33 in theplasma generation region 25 in the X direction and the Y direction bycontrolling the operation of the triaxial stage 226. The shootingcontroller 81 may regard “ΔXp/Kx” obtained by dividing ΔXp calculated inthe step S292 by a constant Kx as the amount of the movement of thelaser beam focusing optical system 22 a in the X direction. The shootingcontroller 81 may regard “ΔYp/Ky” obtained by dividing ΔYp calculated inthe step S292 by a constant Ky as the amount of the movement of thelaser beam focusing optical system 22 a in the Y direction. The shootingcontroller 81 may output the control signal containing ΔXp/Kx and ΔYp/Kyto the triaxial stage 226. By using ΔXp/Kx and ΔYp/Ky obtained bydividing ΔXp and ΔYp by the constant Kx and the constant Ky,respectively, as the amount of the movement of the laser beam focusingoptical system 22 a, it is possible to move the laser beam focusingoptical system 22 a with a high degree of accuracy. Here, the constantKx and the constant Ky may be constants reflecting an optical parameterof the laser beam focusing optical system 22 a. Here, the relationshipof the focused position of the pulsed laser beam 33 and the position ofthe droplet 271 with the position of the plasma light will be describedlater with reference to FIG. 23.

In step S294, the shooting controller 81 may measure the image of theplasma light just after being irradiated with the pulsed laser beam 33.Here, a process for measuring the image of the plasma light will bedescribed later with reference to FIG. 21.

In step S295, the shooting controller 81 may determine whether or notthe focused position of the pulsed laser beam 33 in the X direction andthe Y direction is within an allowable range. When determining that theposition of the plasma light is within the allowable range, the shootingcontroller 81 may regard the focused position of the pulsed laser beam33 as being within the allowable range. The shooting controller 81 maydetermine whether or not ΔXp and ΔYp fulfill all the followingexpressions, based on the focused position of the pulsed laser beam 33after the control in the step S293.|ΔXp|≤ΔXpmax|ΔYp|≤ΔYpmax

When determining that the position of the plasma light is within theallowable range, the shooting controller 81 may regard the focusedposition of the pulsed laser beam 33 as being within the allowablerange, and move the step to step S296. On the other hand, whendetermining that the position of the plasma light is out of theallowable range, the shooting controller 81 may regard the focusedposition of the pulsed laser beam 33 as being out of the allowablerange, and end this process.

In the step S296, the shooting controller 81 may output a control signalto move the target supply part 26 by ΔZp in the Z direction, to thebiaxial stage 74. As described with reference to FIG. 15B, when thefocused position of the pulsed laser beam 33 matches the target positionPdt of the droplet 271, it is possible to efficiently generate plasmalight. Therefore, the shooting controller 81 may move the position ofthe droplet 271 by ΔZp calculated in the step S292 in the Z direction.For this, the shooting controller 81 may move the target supply part 26by ΔZp in the Z direction.

In step S297, the shooting controller 81 may output a control signal tomove the laser beam focusing optical system 22 a in the Z direction, tothe triaxial stage 226. The shooting controller 81 may control thefocused position of the pulsed laser beam 33 in the plasma generationregion 25 in the Z direction by controlling the operation of thetriaxial stage 226. The shooting controller 81 may regard ΔZp calculatedin the step S292 as the amount of the movement of the laser focusingoptical system 22 a in the Z direction. The shooting controller 81 mayoutput the control signal containing ΔZp to the triaxial stage 226.

In step S298, the shooting controller 81 may measure the image of theplasma light just after being irradiated with the pulsed laser beam 33.Here, the process for measuring the image of the plasma light will bedescribed later with reference to FIG. 21.

FIG. 21 is a flowchart showing the process for measuring the image ofthe plasma light in the step S291, the step S294 and the step S298 shownin FIG. 20.

In step S2911, the shooting controller 81 may set the delay time Tds asTds=Tdsb in order to set the imaging timing of the imaging part 422 andthe imaging part 432 to a timing just after the irradiation timing ofthe pulsed laser beam 33.

In step S2912, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texb in order to secure necessaryand sufficient time for which the image sensor 422 a and the imagesensor 432 a capture the image of the plasma light.

In step S2913, the shooting controller 81 may not output a gate signalto the AND circuit 832, that is, the gate signal may be turned off. Bythis means, the light source 421 a and the light source 431 a may notemit pulsed light.

In step S2914, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831. The image measurement unit 42and the image measurement unit 43 may capture the image of the imagingregion 25 a. The captured image may contain the image of the plasmalight emitted from the droplet 271 just after being irradiated with thepulsed laser beam 33 in the plasma generation region 25. The imagemeasurement unit 42 and the image measurement unit 43 may generate theimage data 1 and the image data 2 of the captured image, and output thedata to the shooting controller 81.

In step S2915, the shooting controller 81 may determine whether or notthe image data 1 and the image data 2 can be acquired. When determiningthat the image data 1 and the image data 2 cannot be acquired becausethe image measurement unit 42 and the image measurement unit 43 are notready to output the image data 1 and the image data 2, the shootingcontroller 81 may wait. On the other hand, when determining that theimage data 1 and the image data 2 can be acquired because the imagemeasurement unit 42 and the image measurement unit 43 are ready tooutput the image data 1 and the image data 2, the shooting controller 81may move the step to step S2916.

In the step S2916, the shooting controller 81 may acquire the image data1 and the image data 2 outputted from the image measurement unit 42 andthe image measurement unit 43.

In step S2917, the shooting controller 81 may calculate the position ofthe plasma light emitted from the droplet 271 just after beingirradiated with the pulsed laser beam 33, based on the acquired imagedata 1 and image data 2. Here, a process for calculating the position ofthe plasma light will be described later with reference to FIG. 22.

FIG. 22 is a flowchart showing the process for calculating the positionof the plasma light in the step S2917 shown in FIG. 21.

In step S2917-1, the shooting controller 81 may calculate a measurementposition Cp(Lp, Zp) of the plasma light, based on the image of theplasma light contained in the image data 1 acquired in the step S2916shown in FIG. 21. The image measurement unit 42 may measure the image ofthe plasma light in the normal direction of the L-Z plane. The imagecontained in the image data 1 acquired from the image measurement unit42 may be an image of the plasma light projected onto the L-Z plane.Therefore, the coordinates of the measurement position Cp of the plasmalight, which can be calculated based on the image data 1, may berepresented by an L-component Lp and a Z-component Zp.

In step S2917-2, the shooting controller 81 may calculate a measurementposition Cp(Hp, Zp) of the plasma light, based on the image of theplasma light contained in the image data 2 acquired in the step S2916shown in FIG. 21. The image measurement unit 43 may measure the image ofthe plasma light in the normal direction of the H-Z plane. The imagecontained in the image data 2 acquired from the image measurement unit43 may be an image of the plasma light projected onto the H-Z plane.Therefore, the coordinates of the measurement position Cp of the plasmalight, which can be calculated based on the image data 2, may berepresented by an H-component Hp and the Z-component Zp.

In step S2917-3, the shooting controller 81 may calculate themeasurement position Cp(Xp, Yp, Zp) of the plasma light. The shootingcontroller 81 may calculate the measurement position Cp(Xp, Yp, Zp) ofthe plasma light by the coordinate transformation of the Cp(Lp, Zp)calculated in the step S2917-1, and the Cp(Hp, Zp) calculated in thestep S2917-2.

FIGS. 23A to 23C are drawings each showing the relationship of thefocused position of the pulsed laser beam 33 and the position of thedroplet 271 with the position of the plasma light.

FIG. 23A is a drawing showing a case in which the actual focusedposition of the pulsed laser beam matches the measurement position Cd ofthe droplet 271. In the case shown in FIG. 23A, the measurement positionCp of the plasma light may match the target position Ppt of the plasmalight. Here, as described with reference to FIG. 15B, the coordinates ofthe target position Pdt of the droplet 271 and the target focusedposition of the pulsed laser beam 33 may be shifted from the targetposition Ppt of the plasma light by Zdc in the Z direction. Therefore,as shown in FIG. 23A, both the measurement position Cd of the droplet271 and the actual focused position of the pulsed laser beam 33 may beshifted from the measurement position Cp of the plasma light by Zdp inthe Z direction. Zdp may represent the amount of shifting in themeasured value corresponding to the amount of shifting Zdc in the targetvalue.

FIG. 23B is a drawing showing a case in which the actual focusedposition of the pulsed laser beam is shifted from the measurementposition Cd of the droplet 271 in the −Y direction. In the case shown inFIG. 23B, the measurement position Cp of the plasma light may be shiftedfrom the target position Ppt of the plasma light by ΔYp in the −Ydirection. The reason for this is that the irradiation of the pulsedlaser beam 33 is started at the periphery of the droplet 271 in the −Ydirection side, and therefore the center of the plasma light is shiftedin the −Y direction.

FIG. 23C is a drawing showing a case in which the actual focusedposition of the pulsed laser beam is shifted from the measurementposition Cd of the droplet 271 in the +Y direction. In the case shown inFIG. 23C, the measurement position Cp of the plasma light may be shiftedfrom the target position Ppt of the plasma light by ΔYp in the +Ydirection. The reason for this is that the irradiation of the pulsedlaser beam 33 is started at the periphery of the droplet 271 in the +Ydirection side, and therefore the center of the plasma light is shiftedin the +Y direction.

In this way, when the actual focused position of the pulsed laser beam33 is shifted from the measurement position Cd of the droplet 271 in theY direction, the measurement position Cp of the plasma light may beshifted from the target position Ppt of the plasma light in the Ydirection. The shooting controller 81 may correct the difference in themeasurement position Cp from the target position Ppt of the plasmalight. For this, the shooting controller 81 may move the laser beamfocusing optical system 22 a as described in the step S293 shown in FIG.20, in order to move the focused position of the pulsed laser beam 33.Here, although FIG. 23 shows a case in which the actual focused positionof the pulsed laser beam 33 is shifted from the measurement position Cdof the droplet 271 in the Y direction, the same may apply to a case inwhich the actual focused position of the pulsed laser beam 33 is shiftedin the X direction.

6.3 Effect

The EUV light generation apparatus 1 according to Embodiment 2 canprecisely control the position of the droplet 271 in the plasmageneration region 25. In addition, the EUV light generation apparatus 1can precisely control the focused position of the pulsed laser beam 33.Therefore, the EUV light generation apparatus 1 according to Embodiment2 can substantially match the position of the droplet 271 with thefocused position of the pulsed laser beam 33, and therefore efficientlygenerate plasma light. Consequently, the EUV light generation apparatus1 can efficiently generate the EUV light 252. Moreover, the EUV lightgeneration apparatus 1 according to Embodiment 2 can substantially matchthe position of the plasma light actually emitted in the plasmageneration region 25 with the target position of the plasma lightdetermined according to a command from the exposure apparatus 6.Therefore, the EUV light generation apparatus 1 can stably output theEUV light 252 appropriately generated, to the exposure apparatus 6.

7. Shooting System Using the EUV Light Generation Apparatus According toEmbodiment 3

7.1 Configuration

The shooting system using the EUV light generation apparatus 1 accordingto Embodiment 3 may further include the following components in additionto the components of the shooting system according to Embodiment 2. Thatis, this shooting system may further include a main pulse laser device3, a prepulse laser device 3 b, a wavefront adjustment unit 36, awavefront adjustment unit 37, and a beam combiner 35. The shootingsystem may measure the states of the droplet 271 and the plasma light inthe plasma generation region 25. In addition, the shooting system maycontrol the focused position of the pulsed laser beam 33 outputted fromeach of the main pulse laser device 3 a and the prepulse laser device 3b. Moreover, the shooting system may control the position of the droplet271 reaching the plasma generation region 25 and the position of theplasma light.

Now, the configuration of the shooting system using the EUV lightgeneration apparatus 1 according to Embodiment 3 will be described withreference to FIGS. 24 and 25. FIG. 24 is a drawing showing theconfiguration of the EUV light generation apparatus 1 according toEmbodiment 3. FIG. 25 is a drawing showing the configuration of theshooting system using the EUV light generation apparatus 1 according toEmbodiment 3.

The shooting system using the EUV light generation apparatus 1 accordingto Embodiment 3 may include the main pulse laser device 3 a, theprepulse laser device 3 b, the laser beam focusing optical system 22 a,the biaxial stage 227, the target generator 7, the droplet detector 41,the image measurement unit 42, the image measurement unit 43, thewavefront adjustment unit 36, the wavefront adjustment unit 37, thehigh-reflection mirror 341, the high-reflection mirror 345, the holder343, the holder 346, the beam combiner 35, and the controller 8. Thecontroller 8 may include the shooting controller 81, the delay circuit82, and the image measurement control circuit 83. The configurations ofthe EUV light generation apparatus 1 and the shooting system shown inFIGS. 24 and 25, which are the same as those of the EUV light generationapparatus 1, the image measurement system and the shooting system shownin FIGS. 1 to 3, 5, and 13, are not described again here.

The configuration of the laser beam focusing optical system 22 a shownin FIGS. 24 and 25 may be the same as that of the laser beam focusingoptical system 22 a shown in FIG. 2. The configuration of thehigh-reflection mirrors 341 and 345 shown in FIGS. 24 and 25 may be thesame as that of the high-reflection mirror shown in FIG. 2. Theconfiguration of the holders 343 and 346 shown in FIG. 24 may be thesame as that of the holder 343 shown in FIG. 2. The configuration of thetarget generator 7 shown in FIGS. 24 and 25 may be the same as that ofthe target generator 7 shown in FIG. 13. The configuration of thedroplet detector 41 shown in FIGS. 24 and 25 may be the same as that ofthe droplet detector 41 shown in FIG. 13. The configuration of the imagemeasurement units 42 and 43 shown in FIGS. 24 and 25 may be the same asthat of the image measurement units 42 and 43 shown in FIG. 13. Theconfiguration of the image measurement control circuit 83 shown in FIG.25 may be the same as that of the image measurement control circuit 83shown in FIG. 13.

Here, although FIG. 24 shows an arrangement where the light source part411 and the light receiving part 412 of the droplet detector 41 face oneanother in the Z direction for the sake of convenience, this is by nomeans limiting. The light source part 411 and the light receiving part412 may face one another in the X direction as shown in FIG. 25. Inaddition, although FIG. 24 shows an arrangement where the direction inwhich the light source part 421 and the imaging part 422 of the imagemeasurement unit 42 face one another is orthogonal to the X directionfor the sake of convenience, this is by no means limiting. The directionin which the light source 421 and the imaging part 422 face one anothermay be the H direction as shown in FIG. 25. Moreover, although FIG. 24shows an arrangement where the direction in which the light source part431 and the imaging part 432 face one another is orthogonal to the Xdirection for the sake of convenience, this is by no means limiting. Thedirection in which the light source part 431 and the imaging part 432face one another may be the L direction as shown in FIG. 25.

The configuration of the main pulse laser device 3 a shown in FIGS. 24and 25 may be the same as that of the laser device 3 shown in FIG. 13.The wavelength of a laser beam outputted from the main pulse laserdevice 3 a may be, for example, 10.6 μm. Laser beams outputted from themain pulse laser device 3 a may be referred to as “main pulse laserbeams 31 a to 33 a”, in the same way as described above with referenceto FIG. 1.

The prepulse laser device 3 b shown in FIGS. 24 and 25 may be a solidlaser device such as a YAG laser. The wavelength of a laser beamoutputted from the prepulse laser device 3 b may be, for example, 1.06μm. Laser beams outputted from the prepulse laser device 3 b may bereferred to as “prepulse laser beams 31 b to 33 b” like the main pulselaser beams 31 a to 33 a. The other configuration of the prepulse laserdevice 3 b may be the same as that of the laser device 3 shown in FIG.13.

The prepulse laser beam may be a pulsed laser beam to be emitted to thedroplet 271 before the main pulse laser beam is emitted to the droplet271. Upon being irradiated with the prepulse laser beam, the droplet 271may be broken into a plurality of fine particles of the target 27, anddispersed. The dispersed particles of the target 27 can improve theefficiency of generating EUV light by the main pulse laser beam. Thedispersed particles of the target 27 resulting from irradiating thedroplet 271 with the prepulse laser beam may be referred to as“secondary target 271 a.” Here, a change in the shape of the droplet 271by the irradiation of the main pulse laser beam 33 a or the prepulselaser beam 33 b will be described later with reference to FIG. 26.

The biaxial stage 227 shown in FIGS. 24 and 25 may be provided insteadof the triaxial stage 226 shown in FIG. 2. A plate 225 may be providedon the biaxial stage 227. The biaxial stage 227 may move the plate 225in two directions, the X direction and the Y direction. The biaxialstage 227 may be connected to the shooting controller 81. The biaxialstage 227 may move the plate 225 according to a control signal from theshooting controller 81. By this means, the position and the posture ofthe laser beam focusing optical system 22 a fixed to the plate 225 canbe changed.

The beam combiner 35 shown in FIG. 24 may be an optical systemconfigured to introduce the main pulse laser beam 31 a and the prepulselaser beam 31 b into the chamber 2 through substantially the sameoptical path. The beam combiner 35 may include the high-reflectionmirror 342, the holder 344, a dichroic mirror 351, a holder 352, a tiltstage 353, and a plate 354.

The holder 344 may hold the high-reflection mirror 342. The holder 344holding the high-reflection mirror 342 may be provided on the tilt stage353. The tilt stage 353 on which the holder 344 is provided may be fixedto the plate 354. The tilt stage 353 may rotate the holder 344 about twoaxes, the X-axis and the Y-axis. The tilt stage 353 may move the holder344 in the biaxial directions, the X direction and the Y direction. Thetilt stage 353 may be connected to the shooting controller 81. The tiltstage 353 may move the holder 344 according to a control signal from theshooting controller 81. By this means, it is possible to change theposition and the posture of the high-reflection mirror 342 held by theholder 344.

The holder 352 may hold the dichroic mirror 351. The holder 352 holdingthe dichroic mirror 351 may be fixed to the plate 354.

The high-reflection mirror 342 may be arranged to face the window 21 ofthe chamber 2 and the high-reflection mirror 341. The high-reflectionmirror 342 may reflect the main pulse laser beam 31 a having beenoutputted from the main pulse laser device 3 a and reflected from thehigh-reflection mirror 341, and guide the main pulse laser beam 31 a tothe window 21. The main pulse laser beam 32 a reflected from thehigh-reflection mirror 342 may transmit through the window 21 and beintroduced into the chamber 2.

The dichroic mirror 351 may be formed by coating a diamond substratewith a thin film which allows the main pulse laser beam 31 a to transmittherethrough and reflects the prepulse laser beam 31 b. The dichroicmirror 351 may be arranged to face the window 21 and the high-reflectionmirror 345. The dichroic mirror 351 may be provided on the optical pathof the main pulse laser beam 32 a reflected from the high-reflectionmirror 342. The dichroic mirror 351 may reflect the prepulse laser beam31 b having been outputted from the prepulse laser device 3 b andreflected from the high-reflection mirror 345, and guide the prepulselaser beam 31 b to the window 21. The dichroic mirror 351 may allow themain pulse laser beam 32 a reflected from the high-reflection mirror 342to transmit therethrough and guide the main pulse laser beam 32 a to thewindow 21. In this case, the dichroic mirror 351 may guide the mainpulse laser beam 32 a and the prepulse laser beam 32 b to the window 21through substantially the same optical path.

The wavefront adjustment unit 36 may adjust the wavefront of the mainpulse laser beam 31 a. The wavefront adjustment unit 36 may be arrangedbetween the main pulse laser device 3 a and the high-reflection mirror342 on the optical path of the main pulse laser beam 31 a. Inparticular, the wavefront adjustment unit 36 may be arranged between thehigh-reflection mirror 341 and the high-reflection mirror 342 as shownin FIG. 24. The wavefront adjustment unit 36 may include a convex lens361, a concave lens 362, a holder 363, a holder 364, and a single axisstage 365.

The holder 363 may hold the convex lens 361. The holder 364 may hold theconcave lens 362. The holder 364 holding the concave lens 362 may beprovided on the single axis stage 365. The single axis stage 365 maymove the holder 364 in the Y direction which is the direction of theoptical axis of the main pulse laser beam 31 a entering the concave lens362. The single axis stage 365 may be connected to the shootingcontroller 81. The single axis stage 365 may move the holder 364according to a control signal from the shooting controller 81. By thismeans, it is possible to change the distance between the convex lens 361held by the holder 363 and the concave lens 362 held by the holder 364.

By changing the distance between the convex lens 361 and the concavelens 362, it is possible to adjust the wavefront of the main pulse laserbeam 31 a exiting the convex lens 361. By adjusting the wavefront of themain pulse laser beam 31 a, it is possible to adjust the wavefront ofthe main pulse laser beam 33 a. By this means, it is possible to controlthe focused position of the main pulse laser beam 33 a in the plasmageneration region 25 in the Z direction.

The wavefront adjustment unit 37 may adjust the wavefront of theprepulse laser beam 31 b. The wavefront adjustment unit 37 may bearranged between the prepulse laser device 3 b and the dichroic mirror351 on the optical path of the prepulse laser beam 31 b. In particular,the wavefront adjustment unit 37 may be arranged between thehigh-reflection mirror 345 and the dichroic mirror 351 as shown in FIG.24. The wavefront adjustment unit 37 may include a convex lens 371, aconcave lens 372, a holder 373, a holder 374, and a single axis stage375.

The holder 373 may hold the convex lens 371. The holder 374 may hold theconcave lens 372. The holder 374 holding the concave lens 372 may beprovided on the single axis stage 375. The single axis stage 375 maymove the holder 374 in the Y direction which is the direction of theoptical axis of the prepulse laser beam 31 b entering the concave lens372. The single axis stage 375 may be connected to the shootingcontroller 81. The single axis stage 375 may move the holder 374according to a control signal from the shooting controller 81. By thismeans, it is possible to change the distance between the convex lens 371held by the holder 373 and the concave lens 372 held by the holder 374.

By changing the distance between the convex lens 371 and the concavelens 372, it is possible to adjust the wavefront of the prepulse laserbeam 31 b exiting the convex lens 371. By adjusting the wavefront of theprepulse laser beam 31 b, it is possible to adjust the wavefront of theprepulse laser beam 33 b. By this means, it is possible to control thefocused position of the prepulse laser beam 33 b in the plasmageneration region 25 in the Z direction.

The shooting controller 81 shown in FIGS. 24 and 25 may output a controlsignal to the biaxial stage 227 to control the position and posture ofthe laser beam focusing optical system 22 a. The shooting controller 81may output a control signal to the tilt stage 353 to control theposition and the posture of the high-reflection mirror 342. The shootingcontroller 81 may output a control signal to the single axis stage 365to control the operation of the wavefront adjustment unit 36 includingthe single axis stage 365. The shooting controller 81 may output acontrol signal to the single axis stage 375 to control the operation ofthe wavefront adjustment unit 37 including the single axis stage 375.

The shooting controller 81 may be connected to the main pulse laserdevice 3 a and the prepulse laser device 3 b via the delay circuit 82.Here, the delay time Tdl set in the delay circuit 82 by the shootingcontroller 81, which defines the timing at which a trigger signal isoutputted to the main pulse laser device 3 a, is referred to as “delaytime Tdlm.” Meanwhile, the delay time Tdl set in the delay circuit 82 bythe shooting controller 81, which defines the timing at which a triggersignal is outputted to the prepulse laser device 3 b, is referred to as“delay time Tdlp.” The other configurations of the shooting controller81 and the delay circuit 82 may be the same as those of the shootingcontroller 81 and the delay circuit 82 shown in FIG. 13.

FIGS. 26A to 26D are drawings showing the state in which the shape ofthe droplet 271 is changed by irradiating the droplet 271 with the mainpulse laser beam 33 a or the prepulse laser beam 33 b.

FIG. 26A is a drawing showing the state just before the droplet 271 isirradiated with the prepulse laser beam 33 b. FIG. 26A shows the statebefore the droplet 271 is irradiated with the main pulse laser beam 33 aand the prepulse laser beam 33 b, and therefore the droplet 271 may havethe original shape. The shooting controller 81 may match the focusedposition of the prepulse laser beam 33 b with the center position of thedroplet 271. The beam diameter of the focused prepulse laser beam 33 bmay be equal to or greater than the diameter of the droplet 271. Thediameter of the droplet 271 may be, for example, about 20 μm. The beamdiameter of the focused prepulse laser beam 33 b may be, for example,about 20 μm to 70 μm.

FIG. 26B shows the state just after the droplet 271 is irradiated withthe prepulse laser beam 33 b. In the case shown in FIG. 26B, theabrasion of the droplet 271 due to the irradiation of the prepulse laserbeam 33 b is started at the periphery of the droplet 271 to which theprepulse laser beam 33 b is applied. The reaction of this abrasion maygenerate thrust that allows the droplet 271 to move in the Z directionwhich is the irradiation direction of the prepulse laser beam 33 b.

FIG. 26C is a drawing showing the state just before the secondary target271 a is irradiated with the main pulse laser beam 33 a. In the caseshown in FIG. 26C, due to the reaction of the abrasion, the droplet 271may be turned into the secondary target 271 a and dispersed. Thesecondary target 271 a may be an aggregation of a plurality of fineparticles of the target 27 produced from one droplet 271. The centerposition of the secondary target 271 a may be the center position of thespatial distribution of the fine particles. The secondary target 271 amay be formed in an approximately discoid shape. The cross section ofthe secondary target 271 a in parallel to the Z direction may be formedin an approximately oval shape. When the focused position of theprepulse laser beam 33 b matches the center position of the droplet 271,the irradiation of the prepulse laser beam 33 b is started at the centerof the periphery of the droplet 271 in the −Z direction side. Therefore,the droplet 271 irradiated with the prepulse laser beam 33 b may beabraded, and consequently turned into a plurality of fine particles ofthe target 27, and then dispersed in an approximately discoid shapehaving the central axis approximately parallel to the Z direction. Thatis, when the focused position of the prepulse laser beam 33 b matchesthe center position of the droplet 271, the secondary target 271 a maybe formed in an approximately discoid shape having the central axisapproximately parallel to the Z direction.

In addition, the secondary target 271 a is produced from the droplet 271traveling through the target traveling path 272, and therefore canmaintain the inertia force of the droplet 271 to travel in the Ydirection. Therefore, the thrust in the Z direction due to the abrasionand the inertia force in the Y direction may act on the secondary target271 a. Therefore, the center of the secondary target 271 a may move fromthe center of the droplet 271 in the Z direction and the Y direction.The shooting controller 81 may substantially match the focused positionof the main pulse laser beam 33 a with the center position of the movedsecondary target 271 a. The beam diameter of the focused main pulselaser beam 33 a may be equal to or greater than the diameter of thesecondary target 271 a. The diameter of the secondary target 271 a maybe, for example, about 300 μm to 400 μm. Also the beam diameter of thefocused main pulse laser beam 33 a may be, for example, about 300 μm to400 μm.

FIG. 26D is a drawing showing the state just after the secondary target271 a is irradiated with the main pulse laser beam 33 a. In the caseshown in FIG. 26D, the secondary target 271 a may be turned into plasmaand emit plasma light by irradiating the secondary target 271 a with themain pulse laser beam 33 a. The center of the plasma light may belocated at or near the periphery of the secondary target 271 a to whichthe main pulse laser beam 33 a is applied, in the same way as describedabove with reference to FIG. 15B. Therefore, the center of the plasmalight may be shifted from the center of the secondary target 271 a inthe −Z direction.

Here, the measured value for the center position of the droplet 271 justbefore being irradiated with the prepulse laser beam 33 b may berepresented as “measurement position Cd(Xd, Yd, Zd) of the droplet 271.”The measured value for the center position of the secondary target 271 ajust before being irradiated with the main pulse laser beam 33 a may berepresented as “measurement position Cs(Xs, Ys, Zs) of the secondarytarget 271 a.” The measured value for the center position of the plasmalight emitted from the secondary target 271 a just after beingirradiated with the main pulse laser beam 33 a may be represented as“measurement position Cpm (Xpm, Ypm, Zpm) of the plasma light.” Theshooting controller 81 may store the relationship of the relativepositions of Cd, Cs and Cpm in advance.

7.2 Operation

Now, the operations of the shooting system using the EUV lightgeneration apparatus 1 according to Embodiment 3 will be described withreference to FIGS. 27 to 41. The operations of the shooting system usingthe EUV light generation apparatus 1 according to Embodiment 3, whichare the same as those of the EUV light generation apparatus 1 shown inFIGS. 2 and 3, the image measurement system according to Embodiment 1,and the shooting system according to Embodiment 2, will not be describedagain here. First, the timing control for the image measurementperformed by the shooting system using the EUV light generationapparatus 1 according to Embodiment 3 will be described with referenceto FIGS. 27 to 29.

FIG. 27 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 25, where the image of the droplet 271 justbefore being irradiated with the prepulse laser beam 33 b is measured.

With the time chart shown in FIG. 27, the shooting controller 81 may setthe shutter opening time Texas Tex=Texc in the one-shot circuit 835 inadvance. The shutter opening time Texc may be a period of time which isnecessary and sufficient to capture the image of the droplet 271. Theshutter opening time Texc may be equal to the above-described shutteropening time Texa.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsc in the delay circuit 833. When the image of the droplet 271just before being irradiated with the prepulse laser beam 33 b iscaptured, the imaging timing of the imaging part 422 and the imagingpart 432 may be defined as follows. A summed value “Tdsc+Texc” of thedelay time Tdsc that defines the output timing of the shutter openingsignal and the shutter opening time Texc may be equal to or smaller thana value “delay time Tdlp+time α1” that defines the irradiation timing ofthe prepulse laser beam 33 b. The delay time Tdsc may be calculatedaccording to the following equation.Tdsc=(d/v)−Texc

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIGS. 6 and 7.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on the droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 27, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831.

Then, as shown in FIG. 27, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement.

Then, as shown in FIG. 27, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 833, the delay circuit 833 may outputthe enable signal to the one-shot circuit 835 at the timing delayed bythe delay time Tdsc. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 834, the delay circuit 834 may outputthe enable signal to the one-shot circuit 836 at the timing delayed bythe delay time Tdi.

Then, as shown in FIG. 27, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals each having the pulse width of the exposure time Tr tothe image sensor 422 a and the image sensor 432 a. The image sensor 422a and the image sensor 432 a may be exposed to the light from when theimage sensor exposure signals are inputted until the exposure time Trhas elapsed.

Then, as shown in FIG. 27, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the prepulse laser device 3 b at the timing delayed by thedelay time Tdlp. After a time α1 has elapsed from when the triggersignal is inputted to the prepulse laser device 3 b, the prepulse laserdevice 3 b may emit the prepulse laser beam 33 b to the plasmageneration region 25. Then, when the droplet detection signal isinputted to the delay circuit 82, the delay circuit 82 may output atrigger signal to the main pulse laser device 3 a at the timing delayedby the delay time Tdlm. After a time α2 has elapsed from when thetrigger signal is inputted to the main pulse laser device 3 a, the mainpulse laser device 3 a may emit the main pulse laser beam 33 a to theplasma generation region 25.

Then, as shown in FIG. 27, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texc tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals. The shutter 422 d and the shutter 432 d may be open from whenthe shutter opening signals are inputted until the shutter opening timeTexc has elapsed.

Then, as shown in FIG. 27, when the output signal from the one-shotcircuit 835 and the gate signal are inputted to the AND circuit 832, theAND circuit 832 may output lighting signals each having the pulse widthof the shutter opening time Texc to the light source 421 a and the lightsource 431 a. The gate signal may be outputted from the shootingcontroller 81 to the AND circuit 832 before the one-shot circuit 835outputs the output signal to the AND circuit 832. The light source 421 aand the light source 431 a may emit pulsed light from when the lightingsignals are inputted until the shutter opening time Texc has elapsed.

Then, as shown in FIG. 27, the plasma light may be emitted after theshutter opening time Texc has elapsed. The plasma light may be emittedwhen the secondary target 271 a is irradiated with the main pulse laserbeam 33 a. In addition, the plasma light with a low intensity may beemitted when the droplet 271 is irradiated with the prepulse laser beam33 b. The timing at which this plasma light with a low intensity isemitted may also be a timing just after the shutter opening time Texchas elapsed. The imaging part 422 and the imaging part 432 may capturethe image of the droplet 271 just before being irradiated with theprepulse laser beam 33 b.

Then, as shown in FIG. 27, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the droplet 271 just before being irradiated with theprepulse laser beam 33 b. The shooting controller 81 may calculate themeasurement position Cd(Xd, Yd, Zd) of the droplet 271, based on theacquired image data 1 and image data 2.

The image of the droplet 271 just before being irradiated with theprepulse laser beam 33 b may be the image, for example, as shown in FIG.27.

FIG. 28 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 25, where the image of the droplet 271 justbefore being irradiated with the main pulse laser beam 33 a is measured.

With the time chart shown in FIG. 28, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texd in the one-shot circuit 835 inadvance. The shutter opening time Texd may be a period of time which isnecessary and sufficient to capture the image of the secondary target271 a.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsd in the delay circuit 833. When the image of the secondarytarget 271 a just before being irradiated with the main pulse laser beam33 a is captured, the imaging timing of the imaging part 422 and theimaging part 432 may be defined as follows. A summed value “Tdsd+Texd”of the delay time Tdsd that defines the output timing of the shutteropening signal and the shutter opening time Texd may be equal to orsmaller than a value “delay time Tdlm+time α2” that defines theirradiation timing of the main pulse laser beam 33 a.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIG. 27.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on the droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 28, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831.

Then, as shown in FIG. 28, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement.

Then, as shown in FIG. 28, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 833, the delay circuit 833 may outputthe enable signal to the one-shot circuit 835 at the timing delayed bythe delay time Tdsd. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 834, the delay circuit 834 may outputthe enable signal to the one-shot circuit 836 at the timing delayed bythe delay time Tdi.

Then, as shown in FIG. 28, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals each having the pulse width of the exposure time Tr tothe image sensor 422 a and the image sensor 432 a. The image sensor 422a and the image sensor 432 a may be exposed to the light from when theimage sensor exposure signals are inputted until the exposure time Trhas elapsed.

Then, as shown FIG. 28, when the droplet detection signal is inputted tothe delay circuit 82, the delay circuit 82 may output a trigger signalto the prepulse laser device 3 b at the timing delayed by the delay timeTdlp. After the time α1 has elapsed from when the trigger signal isinputted to the prepulse laser device 3 b, the prepulse laser device 3 bmay emit the prepulse laser beam 33 b to the plasma generation region25. In addition, when the droplet detection signal is inputted to thedelay circuit 82, the delay circuit 82 may output a trigger signal tothe main pulse laser device 3 a at the timing delayed by the delay timeTdlm. After the time α2 has elapsed from when the trigger signal isinputted to the main pulse laser device 3 a, the main pulse laser device3 a may emit the main pulse laser beam 33 a to the plasma generationregion 25.

Then, as shown in FIG. 28, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texd tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals. The shutter 422 d and the shutter 432 d may be open from whenthe shutter opening signals are inputted until the shutter opening timeTexd has elapsed.

Then, as shown in FIG. 28, when the output signal from the one-shotcircuit 835 and the gate signal are inputted to the AND circuit 832, theAND circuit 832 may output lighting signals each having the pulse widthof the shutter opening time Texd to the light source 421 a and the lightsource 431 a. The gate signal may be outputted from the shootingcontroller 81 to the AND circuit 832 before the one-shot circuit 835outputs the output signal to the AND circuit 832. The light source 421 aand the light source 431 a may emit pulsed light from when the lightingsignals are inputted until the shutter opening time Texd has elapsed.

Then, as shown in FIG. 28, the plasma light may be emitted after theshutter opening time Texd has elapsed, from the secondary target 271 airradiated with the main pulse laser beam 33 a. The imaging part 422 andthe imaging part 432 may capture the image of the secondary target 271 ajust before being irradiated with the main pulse laser beam 33 a.

Then, as shown in FIG. 28, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the secondary target 271 a just before being irradiatedwith the main pulse laser beam 33 a. The shooting controller 81 maycalculate the measurement position Cs(Xs, Ys, Zs) of the secondarytarget 271 a, based on the acquired image data 1 and image data 2.

The image of the secondary target 271 a just before being irradiatedwith the main pulse laser beam 33 a may be the image, for example, asshown in FIG. 28.

FIG. 29 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 25, where the image of the plasma lightemitted from the secondary target 271 a just after being irradiated withthe main pulse laser beam 33 a is measured.

With the time chart shown in FIG. 29, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texe in the one-shot circuit 835 inadvance. The shutter opening time Texe may be a period of time which isnecessary and sufficient to capture the image of the plasma light.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdse in the delay circuit 833. When the image of the plasma lightemitted from the secondary target 271 a just after being irradiated withthe main pulse laser beam 33 a is captured, the imaging timing of theimaging part 422 and the imaging part 432 may be defined as follows. Asummed value “Tdse+Texe” of the delay time Tdse that defines the outputtiming of the shutter opening signal and the shutter opening time Texemay be equal to or greater than a value “delay time Tdlm+time α2” thatdefines the irradiation timing of the main pulse laser beam 33 a.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIGS. 27 and 28.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on the droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 29, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831.

Then, as shown in FIG. 29, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement.

Then, as shown in FIG. 29, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 833, the delay circuit 833 may outputthe enable signal to the one-shot circuit 835 at the timing delayed bythe delay time Tdse. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 834, the delay circuit 834 may outputthe enable signal to the one-shot circuit 836 at the timing delayed bythe delay time Tdi.

Then, as shown in FIG. 29, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals each having the pulse width of the exposure time Tr tothe image sensor 422 a and the image sensor 432 a. The image sensor 422a and the image sensor 432 a may be exposed to the light from when theimage sensor exposure signals are inputted until the exposure time Trhas elapsed.

Then, as shown in FIG. 29, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the prepulse laser device 3 b at the timing delayed by thedelay time Tdlp. After the time α1 has elapsed from when the triggersignal is inputted to the prepulse laser device 3 b, the prepulse laserdevice 3 b may emit the prepulse laser beam 33 b to the plasmageneration region 25. In addition, when the droplet detection signal isinputted to the delay circuit 82, the delay circuit 82 may output atrigger signal to the main pulse laser device 3 a at the timing delayedby the delay time Tdlm. After the time α2 has elapsed from when thetrigger signal is inputted to the main pulse laser device 3 a, the mainpulse laser device 3 a may emit the main pulse laser beam 33 a to theplasma generation region 25.

Then, as shown in FIG. 29, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texe tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals. The shutter 422 d and the shutter 432 d may be open from whenthe shutter opening signals are inputted until the shutter opening timeTexe has elapsed.

Then, as shown in FIG. 29, the AND circuit 832 may not output lightingsignals to the light source 421 a and the light source 431 a. When theimage of the plasma light is captured, the shooting controller 81 maynot output a gate signal to the AND circuit 832.

Then, as shown in FIG. 29, the plasma light may be emitted during theshutter opening time Texe. The imaging part 422 and the imaging part 432may capture the image of the plasma light emitted from the secondarytarget 271 a just after being irradiated with the main pulse laser beam33 a.

Then, as shown in FIG. 29, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the plasma light emitted from the secondary target 271 ajust after being irradiated with the main pulse laser beam 33 a. Theshooting controller 81 may calculate the measurement position Cpm (Xpm,Ypm, Zpm) of the plasma light, based on the acquired image data 1 andimage data 2.

The image of the plasma light emitted from the secondary target 271 ajust after being irradiated with the main pulse laser beam 33 a may bethe image, for example, as shown in FIG. 29.

Next, with reference to FIGS. 30 to 41, a process for the shootingcontrol of the shooting system using the EUV light generation apparatus1 according to Embodiment 3 will be described. FIG. 30 is a flowchartshowing a process for the shooting control performed by the shootingcontroller 81 shown in FIG. 25.

In step S41, the shooting controller 81 may output an NG signal to theexposure apparatus controller 61 via the EUV light generation controller5.

In step S42, the shooting controller 81 may read the target positionPpt(Xpt, Ypt, Zpt) of the plasma light. The target position Ppt(Xpt,Ypt, Zpt) of the plasma light may be a target value for the centerposition of the plasma light emitted from the secondary target 271 ajust after being irradiated with the main pulse laser beam 33 a in theplasma generation region 25. The shooting controller 81 may read thetarget position Ppt (Xpt, Ypt, Zpt) of the plasma light stored in theEUV light generation controller 5.

In step S43, the shooting controller 81 may calculate the targetposition Pdt of the droplet 271 and the target position Pst of thesecondary target 271 a. The target position Pst(Xst, Yst, Zst) of thesecondary target 271 a may be a target value for the center position ofthe secondary target 271 a generated in the plasma generation region 25.In particular, the target position Pst(Xst, Yst, Zst) of the secondarytarget 271 a may be a target value for the center position of thesecondary target 271 a just before being irradiated with the main pulselaser beam 33 a in the plasma generation region 25. The shootingcontroller 81 may calculate the target position Pdt of the droplet 271and the target position Pst of the secondary target 271 a, based on thetarget position Ppt of the plasma light read in the step S42. Here, aprocess for calculating the target position Pdt of the droplet 271 andthe target position Pst of the secondary target 271 a will be describedlater with reference to FIG. 31A.

In step S44, the shooting controller 81 may set the target position Pdtof the droplet 271, and the target focused positions of the main pulselaser beam 33 a and the prepulse laser beam 33 b. The shootingcontroller 81 may set the delay time Tds, the delay time Tdl, and thebiaxial stage 74 to supply the droplet 271 to the target position Pdt ofthe droplet 271 calculated in the step S43. The shooting controller 81may set the biaxial stage 227 and the wavefront adjustment unit 37 tofocus the prepulse laser beam 33 b on the target position Pdt of thedroplet 271 calculated in the step S43. The shooting controller 81 mayset the tilt stage 353 and the wavefront adjustment unit 36 to focus themain pulse laser beam 33 a on the target position Pst of the secondarytarget 271 a calculated in the step S43. Here, a process for setting thetarget position Pdt of the droplet 271 and the target focused positionsof the main pulse laser beam 33 a and the prepulse laser beam 33 b willbe described later with reference to FIG. 32.

In step S45, the shooting controller 81 may determine whether or not thedroplet 271 is being outputted. When determining that the droplet 271 isnot being outputted, the shooting controller 81 may wait. On the otherhand, when determining that the droplet 271 is being outputted, theshooting controller 81 may move the step to step S46.

In the step S46, the shooting controller 81 may control the position ofthe droplet 271. The shooting controller 81 may cause the imagemeasurement unit 42 and the image measurement unit 43 to measure theimage of the droplet 271 just before being irradiated with the prepulselaser beam 33 b in the plasma generation region 25. Then, the shootingcontroller 81 may calculate the measurement position Cd(Xd, Yd, Zd) ofthe droplet 271, based on the acquired image data. Then, the shootingcontroller 81 may appropriately modify and set the delay time Tds andthe delay time Tdl and control the operation of the biaxial stage 74,based on the calculated measurement position Cd(Xd, Yd, Zd) of thedroplet 271. Here, a process for controlling the position of the droplet271 will be described later with reference to FIG. 33.

In step S47, the shooting controller 81 may determine whether or not theposition of the droplet 271 is within an allowable range. The shootingcontroller 81 may determine whether or not the measurement positionCd(Xd, Yd, Zd) of the droplet 271 after the control in the step S46fulfills all the following expressions.|Xd−Xdt|≤ΔXdmax|Yd−Ydt|≤ΔYdmax|Zd−Zdt|≤ΔZdmax

When determining that the position of the droplet 271 is out of theallowable range, the shooting controller 81 may move the step to thestep S45. On the other hand, when determining that the position of thedroplet 271 is within the allowable range, the shooting controller 81may move the step to step S48.

In the step S48, the shooting controller 81 may determine whether or notthe prepulse laser beam 33 b is being outputted. The shooting controller81 may make the determination by checking if a trigger signal has beeninputted to the prepulse laser device 3 b. When determining that theprepulse laser beam 33 b is not being outputted, the shooting controller81 may move the step to the step S45. On the other hand, whendetermining that the prepulse laser beam 33 b is being outputted, theshooting controller 81 may move the step to step S49.

In the step S49, the shooting controller 81 may control the position ofthe secondary target 271 a. The shooting controller 81 may cause theimage measurement unit 42 and the image measurement unit 43 to measurethe image of the secondary target 271 a just before being irradiatedwith the main pulse laser beam 33 a in the plasma generation region 25.Then, the shooting controller 81 may calculate the measurement positionCs(Xs, Ys, Zs) of the secondary target 271 a, based on the acquiredimage data. Then, the shooting controller 81 may appropriately modifyand set the delay time Tds and the delay time Tdl and control theoperation of the biaxial stage 74, based on the calculated measurementposition Cs(Xs, Ys, Zs) of the secondary target 271 a. Moreover, theshooting controller 81 may control the operations of the biaxial stage227 and the wavefront adjustment unit 37, based on the calculatedmeasurement position Cs(Xs, Ys, Zs) of the secondary target 271 a. Here,a process for controlling the position of the secondary target 271 awill be described later with reference to FIG. 35.

In step S50, the shooting controller 81 may determine whether or not theposition of the secondary target 271 a is within an allowable range. Theshooting controller 81 may determine whether or not the measurementposition Cs(Xs, Ys, Zs) of the secondary target 271 a after the controlin the step S49 fulfills all the following expressions.|Xs−Xst|≤ΔXsmax|Ys−Yst|≤ΔYsmax|Zs−Zst|≤ΔZsmax

Here, ΔXsmax, ΔYsmax and ΔZsmax in the right-hand side may be thresholdvalues for the respective coordinates that define the allowable range ofthe difference in the measurement position Cs from the target positionPst of the secondary target 271 a. ΔXsmax, ΔYsmax and ΔZsmax may bepredetermined values to efficiently generate plasma light. Whendetermining that the position of the secondary target 271 a is out ofthe allowable range, the shooting controller 81 may move the step to thestep S45. On the other hand, when determining that the position of thesecondary target 271 a is within the allowable range, the shootingcontroller 81 may move the step to step S51.

In the step S51, the shooting controller 81 may determine whether or notthe main pulse laser beam 33 a is being outputted. The shootingcontroller 81 may make the determination by checking if a trigger signalhas been inputted to the main pulse laser device 3 a. When determiningthat the main pulse laser beam 33 a is not being outputted, the shootingcontroller 81 may move the step to the step S45. On the other hand, whendetermining that the main pulse laser beam 33 a is being outputted, theshooting controller 81 may move the step to step S52.

In the step S52, the shooting controller 81 may control the focusedposition of the main pulse laser beam 33 a. The shooting controller 81may cause the image measurement unit 42 and the image measurement unit43 to measure the image of the plasma light emitted from the secondarytarget 271 a just after being irradiated with the main pulse laser beam33 a in the plasma generation region 25. Then, the shooting controller81 may calculate the measurement position Cp(Xp, Yp, Zp) of the plasmalight, based on the acquired image data. Then, the shooting controller81 may control the operations of the tilt stage 353 and the wavefrontadjustment unit 36, based on the calculated measurement position Cp(Xp,Yp, Zp) of the plasma light. In addition, the shooting controller 81 mayappropriately modify and set the delay time Tds and the delay time Tdland control the operation of the biaxial stage 74, based on thecalculated measurement position Cp(Xp, Yp, Zp) of the plasma light.Moreover, the shooting controller 81 may control the operations of thebiaxial stage 227 and the wavefront adjustment unit 37, based on thecalculated measurement position Cp(Xp, Yp, Zp) of the plasma light.Here, a process for controlling the focused position of the main pulselaser beam 33 a will be described later with reference to FIG. 39.

In step S53, the shooting controller 81 may determine whether or not theposition of the plasma light is within an allowable range. The shootingcontroller 81 may determine whether or not the measurement positionCp(Xp, Yp, Zp) of the plasma light fulfills all the followingexpressions, based on the focused position of the main pulse laser beam33 a after the control in the step S52.|Xp−Xpt|≤ΔXpmax|Yp−Ypt|≤ΔYpmax|Zp−Zpt|≤ΔZpmax

When determining that the position of the plasma light is within theallowable range, the shooting controller 81 may move the step to stepS55. On the other hand, when determining that the position of the plasmalight is out of the allowable range, the shooting controller 81 may movethe step to step S54.

In the step S54, the shooting controller 81 may output an NG signal tothe exposure apparatus controller 61 via the EUV light generationcontroller 5. After outputting the NG signal, the shooting controller 81may move the step to the step S45.

In the step S55, the shooting controller 81 may output an OK signal tothe exposure apparatus controller 61 via the EUV light generationcontroller 5.

In step S56, the shooting controller 81 may determine whether or not tostop the process for the shooting control. When determining not to stopthe process for the shooting control, the shooting controller 81 maymove the step to the step S45. On the other hand, when determining tostop the process for the shooting control, the shooting controller 81may end this process.

FIG. 31A is a flowchart showing the process for calculating the targetposition Pdt of the droplet 271 and the target position Pst of thesecondary target 271 a in the step S43 shown in FIG. 30. FIG. 31B is adrawing explaining the process shown in FIG. 31A.

In step S431, the shooting controller 81 may calculate each of thecoordinates of the target position Pdt(Xdt, Ydt, Zdt) of the droplet271. The shooting controller 81 may calculate the target positionPdt(Xdt, Ydt, Zdt) of the droplet 271 according to the followingequations, based on the target position Ppt (Xpt, Ypt, Zpt) of theplasma light read in the step S42 shown in FIG. 30.Xdt=XptYdt=Ypt−YdpZdt=Zpt−ZdpThe shooting controller 81 may regard the X-component Xpt of the targetposition Ppt of the plasma light as the same as the X-component Xdt ofthe target position Pdt of the droplet 271. The shooting controller 81may regard the coordinate shifted from the Y-component Ypt of the targetposition Ppt of the plasma light by Ydp in the −Y direction as theY-component Ydt of the target position Pdt of the droplet 271. Theshooting controller 81 may regard the coordinate shifted from theZ-component Zpt of the target position Ppt of the plasma light by Zdp inthe −Z direction as the Z-component Zdt of the target position Pdt ofthe droplet 271.

In step S432, the shooting controller 81 may calculate each of thecoordinates of the target position Pst(Xst, Yst, Zst) of the secondarytarget 271 a. The shooting controller 81 may calculate the targetposition Pst (Xst, Yst, Zst) of the secondary target 271 a according tothe following equations, based on the target position Ppt(Xpt, Ypt, Zpt)of the plasma light read in the step S42 shown in FIG. 30.Xst=XptYst=YptZst=Zpt+Zsp

The shooting controller 81 may regard the X-component Xpt of the targetposition Ppt of the plasma light as the same as the X-component Xst ofthe target position Pst of the secondary target 271 a. The shootingcontroller 81 may regard the Y-component Ypt of the target position Pptof the plasma light as the same as the Y-component Yst of the targetposition Pst of the secondary target 271 a. The shooting controller 81may regard the coordinate shifted from the Z-component Zpt of the targetposition Ppt of the plasma light by Zsp in the +Z direction as theZ-component Zst of the target position Pst of the secondary target 271a.

In order to emit the plasma light at the target position Ppt of theplasma light, the shooting controller 81 may substantially match thetarget position Pst of the secondary target 271 a and the target focusedposition of the main pulse laser beam 33 a with the target position Pptof the plasma light. However, the center of the plasma light may beshifted from the center of the secondary target 271 a in the −Zdirection, in the same way as described above with reference to FIGS.15B and 26D. The reason for this is that the irradiation of the mainpulse laser beam 33 a is started at the periphery of the secondarytarget 271 a in the −Z direction side, and therefore the center of theplasma light may be located at or near the periphery. Here, the amountof the shifting of the center of the plasma light from the center of thesecondary target 271 a in the −z direction is defined as “Zsp.”Therefore, as shown in FIG. 31B, the shooting controller 81 may set thetarget position Pst of the secondary target 271 a and the target focusedposition of the main pulse laser beam 33 a as the coordinates shiftedfrom the target position Ppt of the plasma light by Zsp in the +Zdirection.

In addition, as described above with reference to FIG. 26C, the centerof the secondary target 271 a may be shifted from the center of thedroplet 271 in the Z direction and the Y direction. The reason for thismay be that the thrust in the Z direction due to the abrasion and theinertia force retained in the droplet 271 in the Y direction act on thedroplet 271 irradiated with the prepulse laser beam 33 b. Here, theamount of the movement of the secondary target 271 a from the center ofthe droplet 271 in the Z direction is defined as “Zsp+Zdp.” In addition,the amount of the movement of the secondary target 271 a from the centerof the droplet 271 in the Y direction is defined as “Ydp.” Therefore, asshown in FIG. 31B, the shooting controller 81 may regard the coordinatesshifted from the target position Ppt of the plasma light by Zdp in the−Z direction and by Ydp in the −Y direction as the target position Pdtof the droplet 271 and the target focused position of the prepulse laserbeam 33 b.

FIG. 32 is a flowchart showing the process for setting the targetposition Pdt of the droplet 271 and the target focused positions of theprepulse laser beam 33 b and the main pulse laser beam 33 a in the stepS44 shown in FIG. 30.

In step S441, the shooting controller 81 may set the biaxial stage 74such that the position of the droplet 271 supplied to the plasmageneration region 25 in the X direction and the Z direction is thetarget position Pdt of the droplet 271. The shooting controller 81 mayoutput a control signal containing the amount of the movement of thetarget supply part 26 in the X direction and the Z direction, to thebiaxial stage 74.

In step S442, the shooting controller 81 may set the delay time Tds suchthat the position of the droplet 271 supplied to the plasma generationregion 25 in the Y direction is the target position Pdt of the droplet271. Here, the delay time Tds used to measure the image of the droplet271 just before being irradiated with the prepulse laser beam 33 b isreferred to as “delay time Tdsc”. The shooting controller 81 may set thedelay time Tdsc in the delay circuit 833. Meanwhile, the delay time Tdsused to measure the image of the secondary target 271 a just beforebeing irradiated with the main pulse laser beam 33 a is referred to as“delay time Tdsd.” The shooting controller 81 may set the delay timeTdsd in the delay circuit 833. Moreover, the delay time Tds used tomeasure the image of the plasma light emitted from the secondary target271 a just after being irradiated with the main pulse laser beam 33 a isreferred to as “delay time Tdse.” The shooting controller 81 may set thedelay time Tdse in the delay circuit 833.

In step S443, the shooting controller 81 may set the delay time Tdlapplied to the trigger signals for the prepulse laser device 3 b and themain pulse laser device 3 a. To be more specific, the delay time Tdlwhich is applied to the trigger signal for the prepulse laser device 3 bis referred to as “delay time Tdlp.” The shooting controller 81 may setthe delay time Tdlp in the delay circuit 82. Meanwhile, the delay timeTdl which is applied to the trigger signal for the main pulse laserdevice 3 a is referred to as “delay time Tdlm.” The shooting controller81 may set the delay time Tdlm in the delay circuit 82.

In step S444, the shooting controller 81 may set the focused position ofthe prepulse laser beam 33 b in the plasma generation region 25 as thetarget position Pdt(Xdt, Ydt, Zdt) of the droplet 271. The shootingcontroller 81 may control the operation of the biaxial stage 227 suchthat the focused position of the prepulse laser beam 33 b in the Xdirection and the Y direction is represented by Xdt and Ydt of thetarget position Pdt of the droplet 271. The shooting controller 81 mayoutput a control signal containing the amount of the movement of thelaser beam focusing optical system 22 a in the X direction and the Ydirection, to the biaxial stage 227. The shooting controller 81 maycontrol the operation of the wavefront adjustment unit 37 such that thefocused position of the prepulse laser beam 33 b in the Z direction isrepresented by Zdt of the target position Pdt of the droplet 271. Theshooting controller 81 may output a control signal containing the amountof the movement of the holder 374 holding the concave lens 372 to thesingle axis stage 375.

In step S445, the shooting controller 81 may set the focused position ofthe main pulse laser beam 33 a in the plasma generation region 25 as thetarget position Pst(Xst, Yst, Zst) of the secondary target 271 a. Theshooting controller 81 may control the operation of the tilt stage 353such that the focused position of the main pulse laser beam 33 a in theX direction and the Y direction is represented by Xst and Yst of thetarget position Pst of the secondary target 271 a. The shootingcontroller 81 may output a control signal containing the amount of themovement and the amount of the rotation of the high-reflection mirror342 of the beam combiner 35 in the X direction and the Y direction, tothe tilt stage 353. The shooting controller 81 may control the operationof the wavefront adjustment unit 36 such that the focused position ofthe main pulse laser beam 33 a in the Z direction is represented by Zstof the target position Pst of the secondary target 271 a. The shootingcontroller 81 may output a control signal containing the amount of themovement of the holder 364 holding the concave lens 362 to the singleaxis stage 365.

FIG. 33 is a flowchart showing the process for controlling the positionof the droplet 271 in the step S46 shown in FIG. 30.

In step S461, the shooting controller 81 may measure the image of thedroplet 271 just before being irradiated with the pulsed laser beam 33b. Here, a process for measuring the image of the droplet 271 will bedescribed later with reference to FIG. 34.

In step S462, the shooting controller 81 may calculate the differencebetween the target position Pdt and the measurement position Cd of thedroplet 271 for each of the coordinates. The shooting controller 81 maycalculate, for each of the coordinates, the difference between thetarget position Pdt(Xdt, Ydt, Zdt) set in the step S44 shown in FIG. 30and the measurement position Cd(Xd, Yd, Zd) measured in the step S461,according to the following equations.ΔXd=Xdt−XdΔYd=Ydt−YdΔZd=Zdt−Zd

In step S463, the shooting controller 81 may output a control signal tomove the target supply part 26 in the X direction and the Z direction tothe biaxial stage 74. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the X direction and the Z direction, by controlling the operation ofthe biaxial stage 74. The shooting controller 81 may regard ΔXdcalculated in the step S462 as the amount of movement of the targetsupply part 26 in the X direction. The shooting controller 81 may regardΔZd calculated in the step S462 as the amount of movement of the targetsupply part 26 in the Z direction. The shooting controller 81 may outputthe control signal containing ΔXd and ΔZd to the biaxial stage 74.

In step S464, the shooting controller 81 may calculate a time ΔTydrequired to move the droplet 271 by ΔYd. The shooting controller 81 maycalculate ΔTyd by using ΔYd calculated in the step S462, according tothe following equation.ΔTyd=ΔYd/v

Here, v in the right-hand side may be the traveling speed of the droplet271.

In step S465, the shooting controller 81 may modify the delay time Tdscand the delay time Tdsd. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the Y direction by setting the delay time Tds and the delay time Tdl.The shooting controller 81 may calculate the modified delay time Tdscand delay time Tdsd by using ΔTyd calculated in the step S464, accordingto the following equations.Tdsc=Tdsc+ΔTydTdsd=Tdsd+ΔTyd

The shooting controller 81 may set the modified delay time Tdsc anddelay time Tdsd in the delay circuit 833.

In step S466, the shooting controller 81 may modify the delay time Tdlpand the delay time Tdlm. The shooting controller 81 may calculate themodified delay time Tdlp and delay time Tdlm by using ΔTyd calculated inthe step S464, according to the following equations.Tdlp=Tdlp+ΔTydTdlm=Tdlm+ΔTyd

The shooting controller 81 may set the modified delay time Tdlp anddelay time Tdlm in the delay circuit 82.

In step S467, the shooting controller 81 may measure the image of thedroplet 271 just before being irradiated with the prepulse laser beam 33b. Here, the process for measuring the image of the droplet 271 will bedescribed later with reference to FIG. 34.

FIG. 34 is a flowchart showing the process for measuring the image ofthe droplet 271 in the step S461 and the step S467 shown in FIG. 33.

In step S4611, the shooting controller 81 may set the delay time Tds inthe delay circuit 833. The shooting controller 81 may set the delay timeTds as Tds=Tdsc in order to set the imaging timing of the imaging part422 and the imaging part 423 to the timing just before the irradiationtiming of the prepulse laser beam 33 b.

In step S4612, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texc in order to secure necessaryand sufficient time for which the image sensor 422 a and the imagesensor 432 a capture the image of the droplet 271.

In step S4613, the shooting controller 81 may output a gate signal tothe AND circuit 832, that is, the gate signal may be turned on. Thelight source 421 a and the light source 431 a may emit pulsed light insynchronization with the imaging timing.

In step S4614, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831. The image measurement unit 42and the image measurement unit 43 may capture the image of the imagingregion 25 a. The captured image may contain the image of the droplet 271just before being irradiated with the prepulse laser beam 33 b in theplasma generation region 25. The image measurement unit 42 and the imagemeasurement unit 43 may generate image data of the captured image, andoutput the data to the shooting controller 81.

In step S4615, the shooting controller 81 may determine whether or notthe image data 1 and the image data 2 can be acquired. When determiningthat the image data 1 and the image data 2 cannot be acquired becausethe image measurement unit 42 and the image measurement unit 43 are notready to output the image data 1 and the image data 2, the shootingcontroller 81 may wait. On the other hand, when determining that theimage data 1 and the image data 2 can be acquired because the imagemeasurement unit 42 and the image measurement unit 43 are ready tooutput the image data 1 and the image data 2, the shooting controller 81may move the step to step S4616.

In the step S4616, the shooting controller 81 may acquire the image data1 and the image data 2 outputted from the image measurement unit 42 andthe image measurement unit 43.

In step S4617, the shooting controller 81 may calculate the position ofthe droplet 271 just before being irradiated with the prepulse laserbeam 33 b, based on the acquired image data 1 and image data 2. Aprocess for calculating the position of the droplet 271 may be the sameas the process shown in FIG. 19, and therefore will not be describedagain here.

FIG. 35 is a flowchart showing the process for controlling the positionof the secondary target 271 a in the step S49 shown in FIG. 30.

In step S491, the shooting controller 81 may measure the image of thesecondary target 271 a just before being irradiated with the main pulselaser beam 33 a. Here, a process for measuring the image of thesecondary target 271 a will be described later with reference to FIG.36.

In step S492, the shooting controller 81 may output a control signal tomove the laser beam focusing optical system 22 a in the X direction andthe Y direction, to the biaxial stage 227. The shooting controller 81may control the focused position of the prepulse laser beam 33 b in theplasma generation region 25 in the X direction and the Y direction, bycontrolling the operation of the biaxial stage 227. The shootingcontroller 81 may regard ΔXsd′/Kx2 obtained by dividing ΔXsd′ calculatedin the step S491 by a constant Kx2 as the amount of movement of thelaser beam focusing optical system 22 a in the X direction. The shootingcontroller 81 may regard ΔYsd′/Ky2 obtained by dividing ΔYsd′ calculatedin the step S491 by a constant Ky2 as the amount of movement of thelaser beam focusing optical system 22 a in the Y direction. The shootingcontroller 81 may output the control signal containing ΔXsd′/Kx2 andΔYsd′/Ky2 to the biaxial stage 227. By using ΔXsd′/Kx2 and ΔYsd′/Ky2 asthe amount of movement of the laser beam focusing optical system 22 a,it is possible to move the laser beam focusing optical system 22 a witha high degree of accuracy. Here, the constant Kx2 and the constant Ky2may be constants reflecting an optical parameter of the laser beamfocusing optical system 22 a.

ΔXsd′ and ΔYsd′ may be the differences between the measurement positionCs of the secondary target 271 a and “virtual position Cd′ of thedroplet 271” in the X direction and the Y direction, respectively. Thevirtual position Cd′ (Xd′, Yd′, Zd′) of the droplet 271 may be aposition of the droplet 271 if the droplet 271 would not have beenirradiated with the prepulse laser beam 33 b. In particular, the virtualposition Cd′ (Xd′, Yd′, Zd′) of the droplet 271 may be a position of thedroplet 271 at the timing just before the droplet 271 is irradiated withthe main pulse laser beam 33 a if the droplet 271 would not have beenirradiated with the prepulse laser beam 33 b. The shooting controller 81may control the position of the secondary target 271 a to allow theplasma light to be efficiently generated, by controlling the focusedposition of the prepulse laser beam 33 b based on ΔXsd′ and ΔYsd′. Here,the virtual position Cd′ of the droplet 271, ΔXsd′ and ΔYsd′ will bedescribed in detail later with reference to FIG. 38.

In step S493, the shooting controller 81 may measure the image of thesecondary target 271 a just before being irradiated with the main pulselaser beam 33 a. Here, the process for measuring the image of thesecondary target 271 a will be described later with reference to FIG.36.

In step S494, the shooting controller 81 may determine whether or notthe focused position of the prepulse laser beam 33 b in the X directionand the Y direction is within an allowable range. When determining thatthe position of the secondary target 271 a is within the allowablerange, the shooting controller 81 may regard the focused position of theprepulse laser beam 33 b as being within the allowable range. Theshooting controller 81 may determine whether or not ΔXsd′ and ΔYsd′fulfill all the following expressions, based on the focused position ofthe prepulse laser beam 33 b after the control in the step S492.|ΔXsd′|≤ΔXsd′max|ΔYsd′|≤ΔYsd′max

Here, ΔXsd′max and ΔYsd′max in the right-hand side may be the thresholdvalues for the respective coordinates that define the allowable range ofthe difference between the measurement position Cs of the secondarytarget 271 a and the virtual position Cd′ of the droplet 271. ΔXsd′maxand ΔYsd′max may be predetermined values to efficiently generate plasmalight. When determining that the position of the secondary target 271 ais within the allowable range, the shooting controller 81 may regard thefocused position of the prepulse laser beam 33 b as being within theallowable range, and move the step to step S495. On the other hand, whendetermining that the position of the secondary target 271 a is out ofthe allowable range, the shooting controller 81 may regard the focusedposition of the prepulse laser beam 33 b as being out of the allowablerange, and end this process.

In the step S495, the shooting controller 81 may calculate thedifference between the target position Pst and the measurement positionCs of the secondary target 271 a for each of the coordinates. Theshooting controller 81 may calculate, for each of the coordinates, thedifference between the target position Pst(Xst, Yst, Zst) set in thestep S44 shown in FIG. 30 and the measurement position Cs(Xs, Ys, Zs)measured in the step S493, according to the following equations.ΔXs=Xst−XsΔYs=Yst−YsΔZs=Zst−Zs

In step S496, the shooting controller 81 may output a control signal tomove the target supply part 26 in the X direction and the Z direction,to the biaxial stage 74. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the X direction and the Z direction, by controlling the operation ofthe biaxial stage 74. The shooting controller 81 may regard ΔXscalculated in the step S495 as the amount of movement of the targetsupply part 26 in the X direction. The shooting controller 81 may regardΔZs calculated in the step S495 as the amount of movement of the targetsupply part 26 in the Z direction. The shooting controller 81 may outputthe control signal containing ΔXs and ΔZs to the biaxial stage 74.

In step S497, the shooting controller 81 may calculate a time ΔTysrequired to move the droplet 271 by ΔYs. The shooting controller 81 maycalculate ΔTys by using ΔYs calculated in the step S495, according tothe following equation.ΔTys=ΔYs/v

Here, v in the right-hand side may be the traveling speed of the droplet271.

In step S498, the shooting controller 81 may modify the delay time Tdscand the delay time Tdsd. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the Y direction by setting the delay time Tds and the delay time Tdl.The shooting controller 81 may calculate the modified delay time Tdscand delay time Tdsd by using ΔTys calculated in the step S497, accordingto the following equations.Tdsc=Tdsc+ΔTysTdsd=Tdsd+ΔTys

The shooting controller 81 may set the modified delay time Tdsc anddelay time Tdsd in the delay circuit 833.

In step S499, the shooting controller 81 may modify the delay time Tdlpand the delay time Tdlm. The shooting controller 81 may calculate themodified delay time Tdlp and delay time Tdlm by using ΔTys calculated inthe step S497, according to the following equations.Tdlp=Tdlp+ΔTysTdlm=Tdlm+ΔTys

The shooting controller 81 may set the modified delay time Tdlp anddelay time Tdlm in the delay circuit 82.

In step S500, the shooting controller 81 may output a control signal tomove the laser beam focusing optical system 22 a in the X direction andthe Y direction, to the biaxial stage 227. The shooting controller 81may control the focused position of the prepulse laser beam 33 b in theplasma generation region 25 in the X direction and the Y direction bycontrolling the operation of the biaxial stage 227. The shootingcontroller 81 may regard ΔXs calculated in the step S495 as the amountof movement of the laser beam focusing optical system 22 a in the Xdirection. The shooting controller 81 may regard ΔYs calculated in thestep S495 as the amount of movement of the laser beam focusing opticalsystem 22 a in the Y direction. The shooting controller 81 may outputthe control signal containing ΔXs and ΔYs to the biaxial stage 227.

In step S501, the shooting controller 81 may control the operation ofthe wavefront adjustment unit 37 to move the focused position of theprepulse laser beam 33 b by ΔZs in the Z direction. The shootingcontroller 81 may control the focused position of the prepulse laserbeam 33 b in the plasma generation region 25 in the Z direction bycontrolling the operation of the wavefront adjustment unit 37. Theshooting controller 81 may convert ΔZs representing the amount ofmovement of the focused position of the prepulse laser beam 33 b intothe amount of movement of the holder 374 holding the concave lens 372 ofthe wavefront adjustment unit 37. The shooting controller 81 may outputthe control signal containing the amount of movement of the holder 374to the single axis stage 375.

In step S502, the shooting controller 81 may measure the image of thesecondary target 271 a just before being irradiated with the main pulselaser beam 33 a. Here, the process for measuring the image of thesecondary target 271 a will be described later with reference to FIG.36.

FIG. 36 is a flowchart showing the process for measuring the image ofthe secondary target 271 a in the step S491, the step S493, and the stepS502 shown in FIG. 35.

In step S4911, the shooting controller 81 may set the delay time Tds inthe delay circuit 833. The shooting controller 81 may set the delay timeTds as Tds=Tdsd in order to set the imaging timing of the imaging part422 and the imaging part 423 to a timing just before the irradiationtiming of the main pulse laser beam 33 a.

In step S4912, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texd in order to secure necessaryand sufficient time for which the image sensor 422 a and the imagesensor 432 a capture the image of the secondary target 271 a.

In step S4913, the shooting controller 81 may output a gate signal tothe AND circuit 832, that is, the gate signal may be turned on. Thelight source 421 a and the light source 431 a may emit pulsed light insynchronization with the imaging timing.

In step S4914, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831. The image measurement unit 42and the image measurement unit 43 may capture the image of the imagingregion 25 a. The captured image may contain the image of the secondarytarget 271 a just before being irradiated with the main pulse laser beam33 a in the plasma generation region 25. The image measurement unit 42and the image measurement unit 43 may generate image data of thecaptured image, and output the data to the shooting controller 81.

In step S4915, the shooting controller 81 may determine whether or notthe image data 1 and the image data 2 can be acquired. When determiningthat the image data 1 and the image data 2 cannot be acquired becausethe image measurement unit 42 and the image measurement unit 43 are notready to output the image data 1 and the image data 2, the shootingcontroller 81 may wait. On the other hand, when determining that theimage data 1 and the image data 2 can be acquired because the imagemeasurement unit 42 and the image measurement unit 43 are ready tooutput the image data 1 and the image data 2, the shooting controller 81may move the step to step S4916.

In the step S4916, the shooting controller 81 may acquire the image data1 and the image data 2 outputted from the image measurement unit 42 andthe image measurement unit 43.

In step S4917, the shooting controller 81 may calculate the position ofthe secondary target 271 a just before being irradiated with the mainpulse laser beam 33 a, based on the acquired image data 1 and image data2. Moreover, the shooting controller 81 may calculate ΔXsd′ and ΔYsd′used in, for example, the step S492 shown in FIG. 35. Here, a processfor calculating the position of the secondary target 271 a will bedescribed later with reference to FIG. 37.

FIG. 37 is a flowchart showing the process for calculating the positionof the secondary target 271 a in the step S4917 shown in FIG. 36.

In step S4917-1, the shooting controller 81 may calculate a measurementposition Cs(Ls, Zs) of the secondary target 271 a, based on the image ofthe secondary target 271 a contained in the image data 1 acquired in thestep S4916 shown in FIG. 36. The image measurement unit 42 may measurethe image of the secondary target 271 a in the normal direction of theL-Z plane. Therefore, the coordinates of the measurement position Cs ofthe secondary target 271 a, which can be calculated based on the imagedata 1, may be represented by an L-component Ls and a Z-component Zs.

In step S4917-2, the shooting controller 81 may calculate a measurementposition Cs(Hs, Zs) of the secondary target 271 a, based on the image ofthe secondary target 271 a contained in the image data 2 acquired in thestep S4916 shown in FIG. 36. The image measurement unit 43 may measurethe image of the secondary target 271 a in the normal direction of theH-Z plane. Therefore, the coordinates of the measurement position Cs ofthe secondary target 271 a, which can be calculated based on the imagedata 2, may be represented by an H-component Hs and the Z-component Zs.

In step S4917-3, the shooting controller 81 may calculate themeasurement position Cs(Xs, Ys, Zs) of the secondary target 271 a. Theshooting controller 81 may calculate the measurement position Cs(Xs, Ys,Zs) of the secondary target 271 a by the coordinate transformation ofCs(Ls, Zs) calculated in the step S4917-1 and Cs(Hs, Zs) calculated inthe step S4917-2.

In step S4917-4, the shooting controller 81 may calculate the virtualposition Cd′ (Xd′, Yd′, Zd′) of the droplet 271. The virtual positionCd′ (Xd′, Yd′, Zd′) of the droplet 271 may be a position of the droplet271 at the timing just before the droplet 271 is irradiated with themain pulse laser beam 33 a if the droplet 271 would not have beenirradiated with the prepulse laser beam 33 b. If the droplet 271 has notbeen irradiated with the prepulse laser beam 33 b, it may be understoodthat the position of the droplet 271 is changed in the Y direction whichis the traveling direction of the droplet 271, but is not changed in theX direction and the Z direction. In this case, it may be understood thatthe droplet 271 moves in the +Y direction at the traveling speed v fromthe irradiation timing of the prepulse laser beam 33 b until theirradiation timing of the main pulse laser beam 33 a. Here, the periodof time from the irradiation timing of the prepulse laser beam 33 buntil the irradiation timing of the main pulse laser beam 33 a may berepresented as Tdx. The shooting controller 81 may calculate the virtualposition Cd′(Xd′, Yd′, Zd′) based on the measurement position Cd(Xd, Yd,Zd) of the droplet 271 calculated in the step S4617 shown in FIG. 34,according to the following equations.Xd′=XdYd′=Yd′+v·TdxZd′=Zd

Here, v·Tdx in the right-hand side may be the distance for which thedroplet travels from the irradiation timing of the prepulse laser beam33 b until the irradiation timing of the main pulse laser beam 33 a.

In step S4917-5, the shooting controller 81 may calculate the differenceΔXsd′ between the measurement position Cs of the secondary target 271 aand the virtual position Cd′ of the droplet 271 in the X direction. Theshooting controller 81 may calculate the difference ΔXsd′ by using themeasurement position Cs of the secondary target 271 a calculated in thestep S4917-3 and the virtual position Cd′ of the droplet 271 calculatedin the step S4917-4, according to the following equation.ΔXsd′=Xs−Xd′

In step S4917-6, the shooting controller 81 may calculate the differenceΔYsd′ between the measurement position Cs of the secondary target 271 aand the virtual position Cd′ of the droplet 271 in the Y direction. Theshooting controller 81 may calculate the difference ΔYsd′ according tothe following equation, in the same way as the step S4917-5.ΔYsd′=Ys−Yd′

FIGS. 38A to 38C are drawings each showing the relationship of thefocused position of the prepulse laser beam 33 b and the position of thedroplet 271 with the position of the secondary target 271 a.

FIG. 38A is a drawing showing a case in which the actual focusedposition of the prepulse laser beam 33 b matches the measurementposition Cd of the droplet 271. In the case shown in FIG. 38A, themeasurement position Cs of the secondary target 271 a matches the targetposition Pst of the secondary target 271 a, as described above withreference to FIG. 31B. This measurement position Cs of the secondarytarget 271 a may match the position to which the virtual position Cd′ ofthe droplet 271 is moved parallel to the +Z direction. That is, thedifference ΔYsd′ in the measurement position Cs of the secondary target271 a from the virtual position Cd′ of the droplet 271 in the Ydirection may be equal to 0 (ΔYsd′=0). Then, the direction of thecentral axis of the secondary target 271 a may be approximately parallelto the Z direction. In the case shown in FIG. 38A, the irradiation ofthe prepulse laser beam 33 b is started at a center of the periphery ofthe droplet 271 in the −Z direction side. Therefore, as described withreference to FIG. 26C, the droplet 271 may be turned into a plurality offine particles of the target 27 and dispersed in an approximatelydiscotic shape having the central axis approximately parallel to the Zdirection.

FIG. 38B shows a case in which the actual focused position of theprepulse laser beam 33 b is shifted from the measurement position Cd ofthe droplet 271 in the −Y direction. In the case shown in FIG. 38B, themeasurement position Cs of the secondary target 271 a may be shifted inthe +Y direction from the position to which the virtual position Cd′ ofthe droplet 271 is moved parallel to the +Z direction. That is, thedifference ΔYsd′ in the measurement position Cs of the secondary target271 a from the virtual position Cd′ of the droplet 271 in the Ydirection may be greater than 0 (ΔYsd′>0). Then, the direction of thecentral axis of the secondary target 271 a may not be approximatelyparallel to the Z direction, but be inclined toward the +Y directionwith respect to the +Z direction. In the case shown in FIG. 38B, theirradiation of the prepulse laser beam 33 b is started at a positionshifted in the −Y direction from the center of the periphery of thedroplet 271 in the −Z direction side. Therefore, the droplet 271 may beturned into a plurality of fine particles of the target 27, anddispersed in an approximately discoid shape having the central axisinclining toward the +Y direction with respect to the +Z direction.

FIG. 38C is a drawing showing a case in which the actual focusedposition of the prepulse laser beam 33 b is shifted from the measurementposition Cd of the droplet 271 in the +Y direction. In the case shown inFIG. 38C, the measurement position Cs of the secondary target 271 a maybe shifted in the −Y direction, from the position to which the virtualposition Cd′ of the droplet 271 is moved parallel to the +Z direction.That is, the difference ΔYsd′ in the measurement position Cs of thesecondary target 271 a from the virtual position Cd′ of the droplet 271in the Y direction may be smaller than 0 (ΔYsd′<0). Then, the directionof the central axis of the secondary target 271 a may not beapproximately parallel to the Z direction, but be inclined toward the −Ydirection with respect to the +Z direction. In the case shown in FIG.38C, the irradiation of the prepulse laser beam 33 b is started at aposition shifted in the +Y direction from the center of the periphery ofthe droplet 271 in the −Z direction side. Therefore, the droplet 271 maybe turned into a plurality of fine particles of the target 27, anddispersed in an approximately discoid shape having the central axisinclining toward the −Y direction with respect to the +Z direction.

As described above, when the actual focused position of the prepulselaser beam 33 b is shifted from the measurement position Cd of thedroplet 271 in the Y direction, the direction of the central axis of thesecondary target 271 a may not be approximately parallel to the Zdirection, but be inclined in the Y direction. In this case, thedistribution of the irradiation energy of the main pulse laser beam 33 aover the periphery of the secondary target 271 a irradiated with themain pulse laser beam 33 a may be uneven, as compared to the case inwhich the direction of the central axis of the secondary target 271 a isapproximately parallel to the Z direction. Therefore, the plasma lightemitted from the secondary target 271 a irradiated with the main pulselaser beam 33 a may have a lower optical intensity and be generated lessstably than the case in which the direction of the central axis of thesecondary target 271 a is approximately parallel to the Z direction. Inother words, the shooting controller 81 can stably generate the plasmalight having a high optical intensity by controlling the focusedposition of the prepulse laser beam 33 b and the measurement position Cdof the droplet 271 such that the direction of the central axis of thesecondary target 271 a is approximately parallel to the Z direction.That is, the shooting controller 81 can more efficiently generate plasmalight from the secondary target 271 a when ΔYsd′ is closer to 0.

For this, the shooting controller 81 may calculate ΔYsd′ in the stepS4917-6 shown in FIG. 37. Then, in order to correct ΔYsd′, the shootingcontroller 81 may move the laser beam focusing optical system 22 a likein the step S492 shown in FIG. 35 to move the focused position of theprepulse laser beam 33 b. Here, although each of FIGS. 38B and 38C showsthe case where the actual focused position of the prepulse laser beam isshifted from the measurement position Cd of the droplet 271 in the Ydirection, the same may apply to another case where the actual focusedposition is shifted in the X direction.

FIGS. 39A and 39B are flowcharts each showing the process forcontrolling the focused position of the main pulse laser beam 33 a inthe step S52 shown in FIG. 30.

In step S521, the shooting controller 81 may measure the image of theplasma light emitted from the secondary target 271 a just after beingirradiated with the main pulse laser beam 33 a. Here, a process formeasuring the image of the plasma light will be described later withreference to FIG. 40.

In step S522, the shooting controller 81 may calculate the differencebetween the measurement position Cs of the secondary target 271 a andthe measurement position Cpm of the plasma light for each of thecoordinates. The shooting controller 81 may calculate, for each of thecoordinates, the difference between the measurement position Cs(Xs, Ys,Zs) measured in the step S49 shown in FIG. 30 and the measurementposition Cpm(Xpm, Ypm, Zpm) measured in the step S521, according to thefollowing equations.ΔXspm=Xs−XpmΔYspm=Ys−Ypm

In step S523, the shooting controller 81 may output a control signal tomove the high-reflection mirror 342 of the beam combiner 35 in the Xdirection and the Y direction, to the tilt stage 353. The shootingcontroller 81 may control the focused position of the main pulse laserbeam 33 a in the plasma generation region 25 in the X direction and theY direction, by controlling the operation of the tilt stage 353. Theshooting controller 81 may regard ΔXspm/Kx3 obtained by dividing ΔXspmcalculated in the step S522 by a constant Kx3 as the amount of movementof the high-reflection mirror 342 in the X direction. The shootingcontroller 81 may regard ΔYspm/Ky3 obtained by dividing ΔYspm calculatedin the step S522 by a constant Ky3 as the amount of movement of thehigh-reflection mirror 342 in the Y direction. The shooting controller81 may output the control signal containing ΔXspm/Kx3 and ΔYspm/Ky3 tothe tilt stage 353. By using ΔXspm/Kx3 and ΔYspm/Ky3 as the amounts ofmovement of the high-reflection mirror 342, it is possible to move thehigh-reflection mirror 342 with a high degree of accuracy. Here, theconstant Kx3 and the constant Ky3 may be constants reflecting an opticalparameter of the laser beam focusing optical system 22 a. Therelationship of the focused position of the main pulse laser beam 33 aand the position of the secondary target 271 a with the position of theplasma light will be described later with reference to FIG. 41.

In step S524, the shooting controller 81 may measure the image of theplasma light emitted from the secondary target 271 a just after beingirradiated with the main pulse laser beam 33 a. Here, the process formeasuring the image of the plasma light will be described later withreference to FIG. 40.

In step S525, the shooting controller 81 may determine whether or notthe focused position of the main pulse laser beam 33 a in the Xdirection and the Y direction is within an allowable range. Whendetermining that the position of the plasma light is within theallowable range, the shooting controller 81 may regard the focusedposition of the main pulse laser beam 33 a as being within the allowablerange. The shooting controller 81 may determine whether or not ΔXspm andΔYspm fulfill all the following expressions, based on the focusedposition of the main pulse laser beam 33 a after the control in the stepS523.|ΔXspm|≤ΔXspmmax|ΔYspm|≤ΔYspmmax

Here, ΔXspmmax and ΔYspmmax in the right-hand side may be the thresholdvalues for the respective coordinates that define the allowable range ofthe difference between the measurement position Cs of the secondarytarget 271 a and the measurement position Cpm of the plasma light.ΔXspmmax and ΔYspmmax may be predetermined values to efficientlygenerate plasma light. When determining that the position of the plasmalight is within the allowable range, the shooting controller 81 mayregard the focused position of the main pulse laser beam 33 a as beingwithin the allowable range, and move the step to step S526. On the otherhand, when determining that the position of the plasma light is out ofthe allowable range, the shooting controller 81 may regard the focusedposition of the main pulse laser beam 33 a as being out of the allowablerange, and end this process.

In the step S526, the shooting controller 81 may calculate thedifference between the target position Ppt and the measurement positionCpm of the plasma light for each of the coordinates. The shootingcontroller 81 may calculate, for each of the coordinates, the differencebetween the target position Ppt (Xpt, Ypt, Zpt) read in the step S42shown in FIG. 30 and the measurement position Cpm(Xpm, Ypm, Zpm)measured in the step S524, according to the following equations.ΔXppm=Xpt−XpmΔYppm=Ypt−YpmΔZppm=Zpt−Zpm

In step S527, the shooting controller 81 may output a control signal tomove the target supply part 26 in the X direction and the Z direction tothe biaxial stage 74. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the X direction and the Z direction, by controlling the operation ofthe biaxial stage 74. The shooting controller 81 may regard ΔXppmcalculated in the step S526 as the amount of movement of the targetsupply part 26 in the X direction. The shooting controller 81 may regardΔZppm calculated in the step S526 as the amount of movement of thetarget supply part 26 in the Z direction. The shooting controller 81 mayoutput the control signal containing ΔXppm and ΔZppm to the biaxialstage 74.

In step S528, the shooting controller 81 may calculate a time ΔTypmrequired to move the droplet 271 by ΔYppm. The shooting controller maycalculate ΔTypm by using ΔYppm calculated in the step S526, according tothe following equation.ΔTypm=ΔYppm/v

Here, v in the right-hand side may be the traveling speed of the droplet271.

In step S529, the shooting controller 81 may modify the delay time Tdscand the delay time Tdsd. The shooting controller 81 may control theposition of the droplet 271 supplied to the plasma generation region 25in the Y direction, by setting the delay time Tds and the delay timeTdl. The shooting controller 81 may calculate the modified delay timeTdsc and delay time Tdsd by using ΔTypm calculated in the step S528,according to the following equations.Tdsc=Tdsc+ΔTypmTdsd=Tdsd+ΔTypm

The shooting controller 81 may set the modified delay time Tdsc anddelay time Tdsd in the delay circuit 833.

In step S530, the shooting controller 81 may modify the delay time Tdlpand the delay time Tdlm. The shooting controller 81 may calculate themodified delay time Tdlp and delay time Tdlm by using ΔTypm calculatedin the step S528, according to the following equations.Tdlp=Tdlp+ΔTypmTdlm=Tdlm+ΔTypm

The shooting controller 81 may set the modified delay time Tdlp anddelay time Tdlm in the delay circuit 82.

In step S531, the shooting controller 81 may output a control signal tomove the laser beam focusing optical system 22 a in the X direction andthe Y direction to the biaxial stage 227. The shooting controller 81 maycontrol the focused position of the prepulse laser beam 33 b in theplasma generation region 25 in the X direction and the Y direction, bycontrolling the operation of the biaxial stage 227. The shootingcontroller 81 may regard ΔXppm calculated in the step S526 as the amountof movement of the laser beam focusing optical system 22 a in the Xdirection. The shooting controller 81 may regard ΔYppm calculated in thestep S526 as the amount of movement of the laser beam focusing opticalsystem 22 a in the Y direction. The shooting controller 81 may outputthe control signal containing ΔXppm and ΔYppm to the biaxial stage 227.

In step S532, the shooting controller 81 may control the operation ofthe wavefront adjustment unit 37 to move the focused position of theprepulse laser beam 33 b by ΔZppm in the Z direction. The shootingcontroller 81 may control the focused position of the prepulse laserbeam 33 b in the plasma generation region 25 in the Z direction, bycontrolling the operation of the wavefront adjustment unit 37. Theshooting controller 81 may convert ΔZppm representing the amount ofmovement of the focused position of the prepulse laser beam 33 b intothe amount of movement of the holder 374 holding the concave lens 372 ofthe wavefront adjustment unit 37. The shooting controller 81 may outputthe control signal containing the amount of movement of the holder 374to the single axis stage 375.

In step S533, the shooting controller 81 may output a control signal tomove the high-reflection mirror 342 of the beam combiner 35 in the Xdirection and the Y direction, to the tilt stage 353. The shootingcontroller 81 may control the focused position of the main pulse laserbeam 33 a in the plasma generation region 25 in the X direction and theY direction, by controlling the operation of the tilt stage 353. Theshooting controller 81 may regard ΔXppm calculated in the step S526 asthe amount of movement of the high-reflection mirror 342 in the Xdirection. The shooting controller 81 may regard ΔYppm calculated in thestep S526 as the amount of movement of the high-reflection mirror 342 inthe Y direction. The shooting controller 81 may output the controlsignal containing ΔXppm and ΔYppm to the tilt stage 353.

In step S534, the shooting controller 81 may control the operation ofthe wavefront adjustment unit 36 to move the focused position of themain pulse laser beam 33 a by ΔZppm in the Z direction. The shootingcontroller 81 may control the focused position of the main pulse laserbeam 33 a in the plasma generation region 25 in the Z direction, bycontrolling the operation of the wavefront adjustment unit 36. Theshooting controller 81 may convert ΔZppm representing the amount ofmovement of the focused position of the main pulse laser beam 33 a intothe amount of movement of the holder 364 holding the concave lens 362 ofthe wavefront adjustment unit 36. The shooting controller 81 may outputthe control signal containing the amount of movement of the holder 364to the single axis stage 365.

In step S535, the shooting controller 81 may measure the image of theplasma light emitted from the secondary target 271 a just after beingirradiated with the main pulse laser beam 33 a. Here, the process formeasuring the image of the plasma light will be described later withreference to FIG. 40.

FIG. 40 is a flowchart showing the process for measuring the image ofthe plasma light in the step S521, the step S524, and the step S535shown in FIGS. 39A and 39B.

In step S5211, the shooting controller 81 may set the delay time Tds inthe delay circuit 833. The shooting controller 81 may set the delay timeTds as Tds=Tdse in order to set the imaging timing of the imaging part422 and the imaging part 432 to a timing just after the irradiationtiming of the main pulse laser beam 33 a.

In step S5212, the shooting controller 81 may set the shutter openingtime Tex in the one-shot circuit 835. The shooting controller 81 may setthe shutter opening time Tex as Tex=Texe in order to secure necessaryand sufficient time for which the image sensor 422 a and the imagesensor 432 a capture the image of the plasma light.

In step S5213, the shooting controller 81 may not output a gate signalto the AND circuit 832, that is, the gate signal may be turned off. Bythis means, the light source 421 a and the light source 431 a may notemit pulsed light.

In step S5214, the shooting controller 81 may output an imagemeasurement signal to the AND circuit 831. The image measurement unit 42and the image measurement unit 43 may capture the image of the imagingregion 25 a. The captured image may contain the image of the plasmalight emitted from the secondary target 271 a just after beingirradiated with the main pulse laser beam 33 a in the plasma generationregion 25. The image measurement unit 42 and the image measurement unit43 may generate image data of the captured image, and output the data tothe shooting controller 81.

In step S5215, the shooting controller 81 may determine whether or notthe image data 1 and the image data 2 can be acquired. When determiningthat the image data 1 and the image data 2 cannot be acquired becausethe image measurement unit 42 and the image measurement unit 43 are notready to output the image data 1 and the image data 2, the shootingcontroller 81 may wait. On the other hand, when determining that theimage data 1 and the image data 2 can be acquired because the imagemeasurement unit 42 and the image measurement unit 43 are ready tooutput the image data 1 and the image data 2, the shooting controller 81may move the step to step S5216.

In the step S5216, the shooting controller 81 may acquire the image data1 and the image data 2 outputted from the image measurement unit 42 andthe image measurement unit 43.

In step S5217, the shooting controller 81 may calculate the position ofthe plasma light emitted from the secondary target 271 a just afterbeing irradiated with the main pulse laser beam 33 a, based on theacquired image data 1 and image data 2. A process for calculating theposition of the plasma light may be the same as the process shown inFIG. 22, and therefore is not described again here.

FIGS. 41A to 41C are drawings each showing the relationship of thefocused position of the main pulse laser beam 33 a and the position ofthe secondary target 271 a with the position of the plasma light.

FIG. 41A is a drawing showing a case in which the actual focusedposition of the main pulse laser beam 33 a matches the measurementposition Cs of the secondary target 271 a. In the case shown in FIG.41A, the measurement position Cpm of the plasma light may match thetarget position Ppt of the plasma light. Here, as described withreference to FIG. 31B, the coordinates of the target position Pst of thesecondary target 271 a and the target focused position of the main pulselaser beam 33 a may be shifted from the target position Ppt of theplasma light by Zsp in the Z direction. As a result, as shown in FIG.41A, both the measurement position CS of the secondary target 271 a andthe actual focused position of the main pulse laser beam 33 a may beshifted from the measurement position Cpm of the plasma light by Zspm inthe Z direction. Zspm may represent the amount of shifting in themeasured value corresponding to the amount of shifting Zsp in the targetvalue. In addition, the beam diameter of the main pulse laser beam 33 amay be equal to the diameter of the secondary target 271 a. Therefore,in the case shown in FIG. 41A, almost the entire periphery of thesecondary target 271 a in the −Z direction side may be irradiated withthe main pulse laser beam 33 a. Consequently, the diameter of the plasmalight may be equal to or greater than the beam diameter of the mainpulse laser beam 33 a.

FIG. 41B shows a case in which the actual focused position of the mainpulse laser beam 33 a is shifted from the measurement position Cs of thesecondary target 271 a in the −Y direction. In the case shown in FIG.41B, the measurement position Cpm of the plasma light may be shiftedfrom target position Ppt of the plasma light in the −Y direction. Thereason for this is that the irradiation of the main pulse laser beam 33a is started at the periphery of the secondary target 271 a in the −Ydirection side, and therefore the center of the plasma light is shiftedin the −Y direction. In addition, in the case shown in FIG. 41B, only aportion of the periphery of the secondary target 271 a in the −Zdirection side may be irradiated with the main pulse laser beam 33 a.Therefore, the diameter of the plasma light may be smaller than thediameter in the case shown in FIG. 41A.

FIG. 41C shows a case in which the actual focused position of the mainpulse laser beam 33 a is shifted from the measurement position Cs of thesecondary target 271 a in the +Y direction. In the case shown in FIG.41C, the measurement position Cpm of the plasma light may be shiftedfrom the target position Ppt of the plasma light in the +Y direction.The reason for this is that the irradiation of the main pulse laser beam33 a is started at the periphery of the secondary target 271 a in the +Ydirection side, and therefore the center of the plasma light is shiftedin the +Y direction. In addition, in the case shown in FIG. 41C, only aportion of the periphery of the secondary target 271 a in the −Zdirection side may be irradiated with the main pulse laser beam 33 a.Therefore, the diameter of the plasma light may be smaller than thediameter in the case shown in FIG. 41A.

As described above, when the actual focused position of the main pulselaser beam 33 a is shifted from the measurement position Cs of thesecondary target 271 a in the Y direction, the measurement position Cpmof the plasma light may be shifted from the target position Ppt of theplasma light in the Y direction. The shooting controller 81 may correctthe difference in the measurement position Cpm from the target positionPpt of the plasma light. For this, in order to move the focused positionof the main pulse laser beam 33 a, the shooting controller 81 may causethe tilt stage 353 to move the high-reflection mirror 342 of the beamcombiner 35 as shown in the step S523 of FIG. 39. Here, although each ofFIGS. 41B and 41C shows the case where the actual focused position ofthe main pulse laser beam 33 a is shifted from the measurement positionCs of the secondary target 271 a in the Y direction, the same may applyto another case where the actual focused position of the main pulselaser beam 33 a is shifted in the X direction.

7.3 Effect

The EUV light generation apparatus 1 according to Embodiment 3 canprecisely control the positions of the droplet 271 and the secondarytarget 271 a in the plasma generation region 25. Moreover, the EUV lightgeneration apparatus 1 can precisely control the focused positions ofthe prepulse laser beam 33 b and the main pulse laser beam 33 a.Therefore, the EUV light generation apparatus 1 according to Embodiment3 can substantially match the position of the droplet 271 with thefocused position of the prepulse laser beam 33 b, and therefore generatethe secondary target 271 a that can efficiently generate plasma light.Moreover, the EUV light generation apparatus 1 can substantially matchthe position of the secondary target 271 a with the focused position ofthe main pulse laser beam 33 a, and therefore efficiently generateplasma light. Consequently, the EUV light generation apparatus 1 canefficiently generate the EUV light 252. Moreover, the EUV lightgeneration apparatus 1 according to Embodiment 3 can substantially matchthe position of the plasma light actually emitted in the plasmageneration region 25 with the target position of the plasma lightdetermined according to a command from the exposure apparatus 6.Consequently, the EUV light generation apparatus 1 can stably output theEUV light 252 to the exposure apparatus 6.

8. Shooting System Using the EUV Light Generation Apparatus According toEmbodiment 4

8.1 Configuration

With the shooting system using the EUV light generation apparatus 1according to Embodiment 3, in order to generate the EUV light 252emitted in a single pulse, one prepulse laser beam and one main pulselaser beam may be introduced into the plasma generation region 25.Meanwhile, with the shooting system using the EUV light generationapparatus 1 according to Embodiment 4, in order to generate the EUVlight 252 emitted in a single pulse, a plurality of prepulse laser beamsand one main pulse laser beam may be introduced into the plasmageneration region 25. Here, with the present embodiment, although thenumber of the plurality of prepulse laser beams is two in thedescription for the sake of convenience, the number of prepulse laserbeams may be three or more.

Among the plurality of prepulse laser beams, a prepulse laser beam whichis first outputted from a prepulse laser device to irradiate the droplet271 may be referred to as “first prepulse laser beam.” Among theplurality of prepulse laser beams, a prepulse laser beam which isoutputted next to the first prepulse laser beam from a prepulse laserdevice may be referred to as “second prepulse laser beam.”

FIGS. 42A to 42D are drawings showing the relationship of the first andsecond prepulse laser beams and the main pulse laser beam with the formof the target 27 irradiated with these laser beams.

When the droplet 271 reaches the plasma generation region 25 in thechamber 2, the shooting system according to Embodiment 4 may irradiatethe droplet 271 with the first prepulse laser beam as shown in FIG. 42A.A beam diameter D1 of the focused first prepulse laser beam may be equalto or greater than the diameter of the droplet 271 in the plasmageneration region 25. The beam diameter D1 may be, for example, about 20μm to 100 μm.

Upon being irradiated with the first prepulse laser beam, the secondarytarget 271 a may be generated from the target 271 as described above. Asshown in FIG. 42B, the secondary target 271 a may be dispersed in adome-like shape. A high-density region where the plurality of atomizedparticles of the target 27 increases in density may be formed in thebottom side of the dome-shaped dispersed secondary target 271 a. Thishigh-density region may be formed in a doughnut shape. A low-densityregion where the plurality of atomized particles of the target 27decreases in density may be formed inside the doughnut-shaped highdensity region. The top region of the dome-shaped dispersed secondarytarget 271 a may be formed in the side in which the droplet 271 isirradiated with the first prepulse laser beam. The low-density regionmay be also formed inside the top region of the dome-shaped secondarytarget 271 a.

As shown in FIG. 42B, the shooting system according to Embodiment 4 mayirradiate the generated secondary target 271 a with the second prepulselaser beam. A beam diameter D2 of the focused second prepulse laser beammay be equal to the outer diameter of the secondary target 271 a in theplasma generation region 25. The beam diameter D2 may be, for example,about 300 μm to 400 μm.

When the secondary target 271 a is irradiated with the second prepulselaser beam, a tertiary target 271 b may be generated from the secondarytarget 271 a. As shown in FIG. 42C, the tertiary target 271 b may begenerated such that the secondary target 271 a is irradiated with thesecond prepulse laser beam and then is transformed. The tertiary target271 b may be an aggregation generated by the irradiation of the secondprepulse laser beam and including a plurality of fine particles of thetargets 27 which are finer than the fine particles of the secondarytarget 271 a, the vapor of the target 27, and a preplasma part of whichhas been turned into plasma. The preplasma may be the target 27containing ions or neutral particles because part of the secondarytarget 271 a is turned into plasma. The preplasma may have a low energynot enough to emit the EUV light 251. The preplasma may develop into theside in which the secondary target 271 a is irradiated with the secondprepulse laser beam.

As shown in FIG. 42C, the shooting system according to Embodiment 4 mayirradiate the generated tertiary target 271 b with the main pulse laserbeam. A beam diameter D3 of the focused main pulse laser beam may beequal to the outer diameter of the tertiary target 271 b in the plasmageneration region 25. The beam diameter D3 may be, for example, about300 μm to 400 μm.

Upon being irradiated with the main pulse laser beam, the tertiarytarget 271 b may emit plasma light as shown in FIG. 42D. The plasmalight may contain the EUV light 251. The tertiary target 271 b maycontain vapor and preplasma, and therefore, when being irradiated withthe main pulse laser beam, the tertiary target 271 b may be efficientlyheated and turned into plasma. By this means, the tertiary target 271 bcontaining vapor and preplasma can improve the efficiency of generatingthe EUV light 251 by the irradiation of the main pulse laser beam.

The shooting system according to Embodiment 4 may have a configurationdifferent from the shooting system according to Embodiment 3 in that twoprepulse laser devices and two wavefront adjustment units are provided.To be more specific, the shooting system according to Embodiment 4 mayinclude a first prepulse laser device 3 c and a second prepulse laserdevice 3 d, instead of the prepulse laser device 3 b of the shootingsystem according to Embodiment 3. In addition, the shooting systemaccording to Embodiment 4 may include a wavefront adjustment unit 38 anda wavefront adjustment unit 39, instead of the wavefront adjustment unit37 of the shooting system according to Embodiment 3. Moreover, theshooting system according to Embodiment 4 may include a high-reflectionmirror 347 and a beam combiner 348, instead of the high-reflectionmirror 345 of the shooting system according to Embodiment 3.

Then, the shooting system according to Embodiment 4 may measure thestates of the target 27 and the plasma light in the plasma generationregion 25. In addition, the shooting system according to Embodiment 4may control the focused position of the pulsed laser beam 33 outputtedfrom each of the first prepulse laser device 3 c, the second prepulselaser device 3 d, and the main pulse laser device 3 a. Moreover, theshooting system according to Embodiment 4 may control the position ofthe target 27 reaching the plasma generation region 25, and the positionof the plasma light.

Now, the configuration of the shooting system using the EUV lightgeneration apparatus 1 according to Embodiment 4 will be described withreference to FIG. 43. FIG. 43 is a drawing showing the configuration ofthe shooting system using the EUV light generation apparatus 1 accordingto Embodiment 4.

The shooting system using the EUV light generation apparatus 1 accordingto Embodiment 4 may include the main pulse laser device 3 a, the firstprepulse laser device 3 c, the second prepulse laser device 3 d, thelaser beam focusing optical system 22 a, the biaxial stage 227, thetarget generator 7, the droplet detector 41, the image measurement unit42, the image measurement unit 43, the wavefront adjustment unit 36, thewavefront adjustment unit 38, the wavefront adjustment unit 39, thehigh-reflection mirror 341, the high-reflection mirrors 342, thehigh-reflection mirror 347, the dichroic mirror 351, the tilt stage 353,the beam combiner 348, and the controller 8. The controller 8 mayinclude the shooting controller 81, the delay circuit 82, and the imagemeasurement control circuit 83. The configurations of the EUV lightgeneration apparatus 1 and the shooting system shown in FIG. 43, whichare the same as the configurations of the EUV light generation apparatus1 according to Embodiment 3 with the image measurement system and theshooting system shown in FIGS. 24 and 25, will not be described againhere.

The configuration of the main pulse laser device 3 a shown in FIG. 43may be the same as that of the main pulse laser device 3 a shown inFIGS. 24 and 25. The configurations of the laser beam focusing opticalsystem 22 a and the biaxial stage 227 shown in FIG. 43 may be the sameas those of the laser beam focusing optical system 22 a and the biaxialstage 227 shown in FIGS. 24 and 25. The configurations of the targetgenerator 7 and the droplet detector 41 shown in FIG. 43 may be the sameas those of the target generator 7 and the droplet detector 41 shown inFIGS. 24 and 25. The configurations of the wavefront adjustment unit 36,the high-reflection mirrors 341 and 342, and the tilt stage 353 shown inFIG. 43 may be the same as those of the wavefront adjustment unit 36,the high-reflection mirrors 341 and 342, and the tilt stage 353 shown inFIGS. 24 and 25. Moreover, the configuration of the image measurementcontrol circuit 83 shown in FIG. 43 may be the same as that of the imagemeasurement control circuit 83 shown in FIGS. 24 and 25.

The first prepulse laser device 3 c shown in FIG. 43 may be provided tooutput the first prepulse laser beam. The first prepulse laser device 3c may be configured to output a pulsed laser beam having a pulse widthon the picosecond or nanosecond time scale. The first prepulse laserdevice 3 c may be formed by a solid laser device, for example, an Nd:YAGlaser and an Nd:YVO₄ laser. In this case, the first prepulse laserdevice 3 c may be configured to convert a laser beam having afundamental wave outputted from the laser device such as an Nd:YAG laserinto a laser beam having a harmonic wave and to output the laser beam.Alternatively, the first prepulse laser device 3 c may be formed by agas laser device such as a CO₂ laser and an excimer laser. The firstprepulse laser device 3 c may be configured to output a linearlypolarized laser beam. Laser beams outputted from the first prepulselaser device 3 c may be referred to as “first prepulse laser beams 31 cto 33 c” in the same way as the main pulse laser beams 31 a to 33 a. Theother configuration of the first prepulse laser device 3 c may be thesame as the configuration of the prepulse laser device 3 b shown inFIGS. 24 and 25.

The second prepulse laser device 3 d shown in FIG. 43 may be provided tooutput the second prepulse laser beam. The second prepulse laser device3 d may be configured to output a pulsed laser beam having a pulse widthon the picosecond or nanosecond time scale. The second prepulse laserdevice 3 d may be formed by a solid laser device, for example, an Nd:YAGlaser and an Nd:YVO₄ laser. In this case, the second prepulse laserdevice 3 d may be configured to convert a laser beam having afundamental wave outputted from the laser device such as an Nd:YAG laserinto a laser beam having a harmonic wave and to output the laser beam.Alternatively, the second prepulse laser device 3 d may be formed by agas laser device such as a CO₂ laser and an excimer laser. The secondprepulse laser device 3 d may be configured to output a linearlypolarized laser beam which is different from the linearly polarizedlaser beam outputted from the first prepulse laser device 3 c. Laserbeams outputted from the second prepulse laser device 3 d may bereferred to as “second prepulse laser beams 31 d to 33 d” in the sameway as the first prepulse laser beams 31 c to 33 c. The otherconfiguration of the second prepulse laser device 3 d may be the same asthe configuration of the prepulse laser device 3 b shown in FIGS. 24 and25.

The wavefront adjustment unit 38 shown in FIG. 43 may adjust thewavefront of the first prepulse laser beam 31 c. The wavefrontadjustment unit 38 may be arranged between the first prepulse laserdevice 3 c and the beam combiner 348 on the optical path of the firstprepulse laser beam 31 c. The other configuration of the wavefrontadjustment unit 38 may be the same as the configuration of the wavefrontadjustment unit 37 shown in FIGS. 24 and 25. That is, the wavefrontadjustment unit 38 may include a convex lens, a concave lens, and asingle axis stage. Then, the distance between the convex lens and theconcave lens of the wavefront adjustment unit 38 may be changed by thecontrol of the shooting controller 81. By this means, it is possible toadjust the wavefront of the first prepulse laser beam 31 c exiting theconvex lens. As a result, it is possible to control the focused positionof the first prepulse laser beam 33 c in the plasma generation region 25in the Z direction shown in FIGS. 44A and 44B.

The wavefront adjustment unit 39 shown in FIG. 43 may adjust thewavefront of the second prepulse laser beam 31 d. The wavefrontadjustment unit 39 may be arranged between the second prepulse laserdevice 3 d and the high-reflection mirror 347 on the optical path of thesecond prepulse laser beam 31 d. The other configuration of thewavefront adjustment unit 39 may be the same as the configuration of thewavefront adjustment unit 37 shown in FIGS. 24 and 25. That is, thewavefront adjustment unit 39 may include a convex lens, a concave lens,and a single axis stage. Then, the distance between the convex lens andthe concave lens of the wavefront adjustment unit 39 may be changed bythe control of the shooting controller 81. By this means, it is possibleto adjust the wavefront of the second prepulse laser beam 31 d exitingthe convex lens. As a result, it is possible to control the focusedposition of the second prepulse laser beam 33 d in the plasma generationregion 25 in the Z direction shown in FIGS. 44C and 44D.

The high-reflection mirror 347 shown in FIG. 43 may be provided on theoptical path of the second prepulse laser beam 31 d to face thewavefront adjustment unit 39 and the beam combiner 348. Thehigh-reflection mirror 347 may reflect the second prepulse laser beam 31d having exited the wavefront adjustment unit 39, and guide the secondprepulse laser beam 31 d to the beam combiner 348. The otherconfiguration of the high-reflection mirror 347 may be the same as theconfiguration of the high-reflection mirror 345 shown in FIGS. 24 and25.

The beam combiner 343 shown in FIG. 43 may be an optical systemconfigured to introduce the first prepulse laser beam 31 c and thesecond prepulse laser beam 31 d to the dichroic mirror 351 throughsubstantially the same optical path. The beam combiner 348 may be, forexample, a polarization beam splitter. The beam combiner 348 may highlyreflect, for example, the first prepulse laser beam 31 c, and allow, forexample, the second prepulse laser beam 31 d to highly transmittherethrough. The beam combiner 348 may be provided on the optical pathof the first prepulse laser beam 31 c to face the wavefront adjustmentunit 38 and the dichroic mirror 351. The beam combiner 348 may beprovided on the optical path of the second prepulse laser beam 31 dhaving been reflected from the high-reflection mirror 347. The beamcombiner 348 may be provided such that the optical axis of the firstprepulse laser beam 31 c substantially matches the optical axis of thesecond prepulse laser beam 31 d.

The first prepulse laser beam 31 c having exited the wavefrontadjustment unit 38 may be reflected from the beam combiner 348 and beguided to the dichroic mirror 351 by the same. Meanwhile, the secondprepulse laser beam 31 d having exited the wavefront adjustment unit 39and been reflected from the high-reflection mirror 347 may transmitthrough the beam combiner 348 and be guided to the dichroic mirror 351.At this time, the beam combiner 348 may guide the first prepulse laserbeam 31 c and the second prepulse laser beam 31 d to the dichroic mirror351 through substantially the same optical path.

The dichroic mirror 351 shown in FIG. 43 may be formed by coating adiamond substrate with a thin film which allows the main pulse laserbeam 31 a to transmit therethrough and reflects the first and secondprepulse laser beams 31 c and 31 d. The dichroic mirror 351 may bearranged to face the window 21 and the beam combiner 348. The dichroicmirror 351 may be provided on the optical path of the main pulse laserbeam 32 a having been reflected from the high-reflection mirror 342.

The dichroic mirror 351 may reflect the first prepulse laser beam 31 cand the second prepulse laser beam 31 d having been guided from the beamcombiner 348 through substantially the same optical path, and guide thefirst prepulse laser beam 31 c and the second prepulse laser beam 31 dto the window 21. The main pulse laser beam 32 a having been reflectedfrom the high-reflection mirror 342 may transmit through the dichroicmirror 351 and be guided to the window 21. At this time, the dichroicmirror 351 may guide the main pulse laser beam 32 a, the first prepulselaser beam 32 c, and the second prepulse laser beam 32 d to the window21 through substantially the same optical path. The other configurationof the dichroic mirror 351 may be the same as that of the dichroicmirror 351 shown in FIGS. 24 and 25.

The image measurement units 42 and 43 shown in FIG. 43 may capture theimage of the imaging region 25 a, and measure the images of the droplet271, the secondary target 271 a, the tertiary target 271 b, and theplasma light. The other configurations of the image measurement units 42and 43 may be the same as those of the image measurement units 42 and 43shown in FIGS. 24 and 25.

The shooting controller 81 shown in FIG. 43 may output a control signalto the single axis stage of the wavefront adjustment unit 38 to controlthe operation of the wavefront adjustment unit 38, including changingthe distance between the convex lens and the concave lens. The shootingcontroller 81 may also output a control signal to the single axis stageof the wavefront adjustment unit 39 to control the operation of thewavefront adjustment unit 39, including changing the distance betweenthe convex lens and the concave lens.

The shooting controller 81 may be connected to the main pulse laserdevice 3 a, the first prepulse laser device 3 c, and the second prepulselaser device 3 d via the delay circuit 82. Here, the delay time Tdl setin the delay circuit 82 by the shooting controller 81, which defines thetiming at which a trigger signal is outputted to the first prepulselaser device 3 c, is referred to also as “delay time Tdlp1.” Meanwhile,the delay time Tdl set in the delay circuit 82 by the shootingcontroller 81, which defines the timing at which a trigger signal isoutputted to the second prepulse laser device 3 d, is referred to alsoas “delay time Tdlp2.” The other configurations of the shootingcontroller 81 and the delay circuit 82 may be the same as those of theshooting controller 81 and the delay circuit 82 shown in FIGS. 24 and25.

FIGS. 44A to 44E are drawings showing the state in which the shape ofthe droplet 271 is changed by the irradiation with the main pulse laserbeam 33 a, the first prepulse laser beam 33 c, and the second prepulselaser beam 33 d.

FIG. 44A is a drawing showing the state of the droplet 271 just beforebeing irradiated with the first prepulse laser beam 33 c. FIG. 44A showsthe state before the droplet 271 is irradiated with the first prepulselaser beam 33 c, and therefore the droplet 271 may have the originalshape. The shooting controller 81 may substantially match the focusedposition of the first prepulse laser beam 33 c with the center positionof the droplet 271.

FIG. 44B is a drawing showing the state of the droplet 271 just afterbeing irradiated with the first prepulse laser beam 33 c. In the caseshown in FIG. 44B, abrasion of the droplet 271 is started at theperiphery of the droplet 271 to which the first prepulse laser beam 33 cis applied. The reaction of this abrasion may generate a thrust thatallows the droplet 271 to move in the Z direction which is theirradiation direction of the first prepulse laser beam 33 c.

FIG. 44C is a drawing showing the state of the secondary target 271 ajust before being irradiated with the second prepulse laser beam 33 d.In the case shown in FIG. 44C, the droplet 271 may be turned into thesecondary target 271 a and dispersed due to the reaction of theabrasion. The secondary target 271 a may be dispersed in a dome-likeshape as described above. The center position of the secondary target271 a may be the center position of the space distribution of the fineparticles dispersed in the dome-like shape. The secondary target 271 ais generated from the droplet 271 traveling through the target travelingpath 272, and therefore can maintain the inertia force of the droplet271 moving in the Y direction. Therefore, the thrust in the Z directiondue to the abrasion and the inertia force in the Y direction may act onthe secondary target 271 a. By this means, the center position of thesecondary target 271 a may be moved from the center position of thedroplet 271, in the Z direction and the Y direction. The shootingcontroller 81 may substantially match the focused position of the secondprepulse laser beam 33 d with the center position of the moved secondarytarget 271 a. Alternatively, the shooting controller 81 may irradiatethe secondary target 271 a with the defocused secondary prepulse laserbeam 33 d. In this case, the optical axis of the defocused secondaryprepulse laser beam 33 d may not pass through the center position of thesecondary target 271 a, as long as the secondary target 271 a fallswithin a beam cross-section of the defocused secondary prepulse laserbeam 33 d. Here, the second prepulse laser beam 33 d and the firstprepulse laser beam 33 c may be substantially coaxial with one another.

FIG. 44D is a drawing showing the state of the tertiary target 271 bjust before being irradiated with the main pulse laser beam 33 a. In thecase shown in FIG. 44D, the secondary target 271 a may be turned intothe tertiary target 271 b due to the irradiation with the secondprepulse laser beam 33 d. The thrust in the Z direction due to theabrasion and the inertia force in the Y direction may act on thetertiary target 271 b in the same way as the secondary target 271 a. Bythis means, the center position of the tertiary target 271 b may bemoved from the center position of the secondary target 271 a, in the Zdirection and the Y direction. The shooting controller 81 maysubstantially match the focused position of the main pulse laser beam 33a with the center position of the moved tertiary target 271 b.Alternatively, the shooting controller 81 may irradiate the tertiarytarget 271 b with the defocused main pulse laser beam 33 a. In thiscase, the optical axis of the defocused main pulse laser beam 33 a maynot pass through the center position of the tertiary target 271 b, buthave a beam cross-section containing the tertiary target 271 b. Here,the main pulse laser beam 33 a and the second prepulse laser beam 33 dmay be substantially coaxial with one another.

FIG. 44E is a drawing showing the state of the plasma light emitted fromthe tertiary target 271 b just after being irradiated with the mainpulse laser beam 33 a. In the case shown in FIG. 44E, the tertiarytarget 271 b may be turned into plasma due to the irradiation with themain pulse laser beam 33 a, and emit plasma light containing the EUVlight 251. The center of the plasma light may be located at or near theperiphery of the tertiary target 271 b to which the main pulse laserbeam 33 a is applied, in the same way as described above with referenceto FIG. 15B. Therefore, the center position of the plasma light may beshifted from the center position of the tertiary target 271 b in the −Zdirection.

Here, the measured value of the center position of the droplet 271 justbefore being irradiated with the first prepulse laser beam 33 c may berepresented as “measurement position Cd(Xd, Yd, Zd) of the droplet 271.”The measured value of the center position of the secondary target 271 ajust before being irradiated with the second prepulse laser beam 33 dmay be represented as “measurement position Cs1(Xs1, Ys1, Zs1) of thesecondary target 271 a.” The measured value of the center position ofthe tertiary target 271 b just before being irradiated with the mainpulse laser beam 33 a may be represented as “measurement position Cs2(Xs2, Ys2, Zs2) of the tertiary target 271 b.” The measured value of thecenter position of the plasma light emitted from the tertiary target 271b just after being irradiated with the main pulse laser beam 33 a may berepresented as “measurement position Cpm (Xpm, Ypm, Zpm) of the plasmalight.” The shooting controller 81 may store the relationship of therelative positions of Cd, Cs1, Cs2, and Cpm in advance.

8.2 Operation

Now, the operations of the shooting system using the EUV lightgeneration apparatus 1 according to Embodiment 4 will be described withreference to FIGS. 45 to 48. The operations of the shooting system usingthe EUV light generation apparatus 1 according to embodiment 4, whichare the same as the operations of the EUV light generation apparatus 1according to Embodiment 3 with the image measurement system and theshooting system shown in FIGS. 24 and 25, will not be described againhere.

First, the timing control for the image measurement performed by theshooting system using the EUV light generation apparatus 1 according toEmbodiment 4 will be described.

FIG. 45 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 43, where the image of the droplet 271 justbefore being irradiated with the first prepulse laser beam 33 c ismeasured.

With the time chart shown in FIG. 45, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texc1 in the one-shot circuit 835 inadvance. The shutter opening time Texc1 may be a period of time which isnecessary and sufficient to capture the image of the droplet 271. Theshutter opening time Texc1 may be equal to the above-described shutteropening time Texa.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsc1 in the delay circuit 833. When the image of the droplet 271just before being irradiated with the first prepulse laser beam 33 c iscaptured, the imaging timing of the imaging part 422 and the imagingpart 432 may be defined as follows. A summed value “Tdsc1+Texc1” of thedelay time Tdsc1 that defines the output timing of the shutter openingsignal and the shutter opening time Texc1 may be equal to or smallerthan a value “delay time Tdlp1+time α11” that defines the irradiationtiming of the first prepulse laser beam 33 c. The delay time Tdsc1 maybe calculated according to the following equation.Tdsc1=(d/v)−Texc1

Here, the time α11 may be a time required from when the delay circuit 82outputs a trigger signal to the first prepulse laser device 3 c untilthe first prepulse laser beam 33 c is focused on the plasma generationregion 25. A time α12 may be a time required from when the delay circuit82 outputs a trigger signal to the second prepulse laser device 3 duntil the second prepulse laser beam 33 d is focused on the plasmageneration region 25. A time α2 may be a time required from when thedelay circuit 82 outputs a trigger signal to the main pulse laser device3 a until the main pulse laser beam 33 a is focused on the plasmageneration region 25.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIGS. 27 to 29.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 45, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831.

Then, as shown in FIG. 45, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement.

Then, as shown in FIG. 45, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 833, the delay circuit 833 may outputthe enable signal to the one-shot circuit 835 at the timing delayed bythe delay time Tdsc1. When the enable signal is inputted from the ANDcircuit 831 to the delay circuit 834, the delay circuit 834 may outputthe enable signal to the one-shot circuit 836 at the timing delayed bythe delay time Tdi.

Then, as shown in FIG. 45, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals each having the pulse width of the exposure time Tr tothe image sensor 422 a and the image sensor 432 a. The image sensor 422a and the image sensor 432 a may be exposed to the light from when theimage sensor exposure signals are inputted until the exposure time Trhas elapsed.

Then, as shown in FIG. 45, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the first prepulse laser device 3 c at the timing delayed bythe delay time Tdlp1. After the time α11 has elapsed from when thetrigger signal is inputted to the first prepulse laser device 3 c, thefirst prepulse laser device 3 c may emit the first prepulse laser beam33 c to the plasma generation region 25. In addition, when the dropletdetection signal is inputted to the delay circuit 82, the delay circuit82 may output a trigger signal to the second prepulse laser device 3 dat the timing delayed by the delay time Tdlp2. After the time a12 haselapsed from when the trigger signal is inputted to the second prepulselaser device 3 d, the second prepulse laser device 3 d may emit thesecond prepulse laser beam 33 d to the plasma generation region 25. Inaddition, when the droplet detection signal is inputted to the delaycircuit 82, the delay circuit 82 may output a trigger signal to the mainpulse laser device 3 a at the timing delayed by the delay time Tdlm.After the time a2 has elapsed from when the trigger signal is inputtedto the main pulse laser device 3 a, the main pulse laser device 3 a mayemit the main pulse laser beam 33 a to the plasma generation region 25.

Then, as shown in FIG. 45, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texc1 tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals. The shutter 422 d and the shutter 432 d may be open from whenthe shutter opening signals are inputted until the shutter opening timeTexc1 has elapsed.

Then, as shown in FIG. 45, when the output signal from the one-shotcircuit 835 and the gate signal are inputted to the AND circuit 832, theAND circuit 832 may output lighting signals each having the pulse widthof the shutter opening time Texc1 to the light source 421 a and thelight source 431 a. The gate signal may be outputted from the shootingcontroller 81 to the AND circuit 832 before the one-shot circuit 835outputs the output signal to the AND circuit 832. The light source 421 aand the light source 431 a may emit pulsed light from when the lightingsignals are inputted until the shutter opening time Texc1 has elapsed.

Then, as shown in FIG. 45, the plasma light may be emitted after theshutter opening time Texc1 has elapsed, from the droplet 271 irradiatedwith the first prepulse laser beam 33 c. The optical intensity of thisplasma light may be lower than the optical intensity of the plasma lightthat is emitted from the tertiary target 271 b irradiated with the mainpulse laser beam 33 a. The imaging part 422 and the imaging part 432 maycapture the image of the droplet 271 just before being irradiated withthe first prepulse laser beam 33 c.

Then, as shown in FIG. 45, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the droplet 271 just before being irradiated with thefirst prepulse laser beam 33 c. The shooting controller 81 may calculatethe measurement position Cd(Xd, Yd, Zd) of the droplet 271, based on theacquired image data 1 and image data 2.

The image of the droplet 271 just before being irradiated with the firstprepulse laser beam 33 c may be, for example, the image as shown in FIG.45.

FIG. 46 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 43, where the image of the secondary target271 a just before being irradiated with the second prepulse laser beam33 d is measured.

With the time chart shown in FIG. 46, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texc2 in the one-shot circuit 835 inadvance. The shutter opening time Texc2 may be a period of time which isnecessary and sufficient to capture the image of the secondary target271 a.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsc2 in the delay circuit 833. When the image of the secondarytarget 271 a just before being irradiated with the second prepulse laserbeam 33 d is captured, the imaging timing of the imaging part 422 andthe imaging part 432 may be defined as follows. A summed value“Tdsc2+Texc2” of the delay time Tdsc2 that defines the output timing ofthe shutter opening signal and the shutter opening time Texc2 may beequal to or smaller than a value “delay time Tdlp2+time α12” thatdefines the irradiation timing of the second prepulse laser beam 33 d.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIG. 45.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 46, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831 in the same way as the case shown in FIG. 45.

Then, as shown in FIG. 46, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement, in the same way asthe case shown in FIG. 45.

Then, as shown in FIG. 46, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834 in the same way as the case shown in FIG. 45. When theenable signal is inputted from the AND circuit 831 to the delay circuit833, the delay circuit 833 may output the enable signal to the one-shotcircuit 835 at the timing delayed by the delay time Tdsc2. When theenable signal is inputted from the AND circuit 831 to the delay circuit834, the delay circuit 834 may output the enable signal to the one-shotcircuit 836 at the timing delayed by the delay time Tdi in the same wayas the case shown in FIG. 45.

Then, as shown in FIG. 46, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals to the image sensor 422 a and the image sensor 432 a inthe same way as the case shown in FIG. 45.

Then, as shown in FIG. 46, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the first prepulse laser device 3 c at the timing delayed bythe delay time Tdlp1 in the same way as the case shown in FIG. 45. Inaddition, when the droplet detection signal is inputted to the delaycircuit 82, the delay circuit 82 may output a trigger signal to thesecond prepulse laser device 3 d at the timing delayed by the delay timeTdlp2 in the same way as the case shown in FIG. 45. Moreover, when thedroplet detection signal is inputted to the delay circuit 82, the delaycircuit 82 may output a trigger signal to the main pulse laser device 3a at the timing delayed by the delay time Tdlm in the same way as thecase shown in FIG. 45.

Then, as shown in FIG. 46, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texc2 tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals, in the same way as the case shown in FIG. 45. The shutter 422 dand the shutter 432 d may be open from when the shutter opening signalsare inputted until the shutter opening time Texc2 has elapsed.

Then, as shown in FIG. 46, when the output signal from the one-shotcircuit 835 and the gate signal are inputted to the AND circuit 832, theAND circuit 832 may output lighting signals each having the pulse widthof the shutter opening time Texc2 to the light source 421 a and thelight source 431 a, in the same way as the case shown in FIG. 45. Thegate signal may be outputted from the shooting controller 81 to the ANDcircuit 832 before the one-shot circuit 835 outputs the output signal tothe AND circuit 832 in the same way as the case shown in FIG. 45. Thelight source 421 a and the light source 431 a may emit pulsed light fromwhen the lighting signals are inputted until the shutter opening timeTexc2 has elapsed.

Then, as shown in FIG. 46, plasma light may be emitted after the shutteropening time Texc2 has elapsed, from the droplet 271 irradiated with thesecond prepulse laser beam 33 d. This plasma light may be emitted fromthe preplasma contained in the secondary target 271 a. The opticalintensity of this plasma light may be lower than the optical intensityof the plasma light that is emitted from the tertiary target 271 birradiated with the main pulse laser beam 33 a. The imaging part 422 andthe imaging part 432 may capture the image of the secondary target 271 ajust before being irradiated with the second prepulse laser beam 33 d.

Then, as shown in FIG. 46, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the secondary target 271 a just before being irradiatedwith the second prepulse laser beam 33 d. The shooting controller 81 maycalculate the measurement position Cs1(Xs1, Ys1, Zs1) of the secondarytarget 271 a, based on the acquired image data 1 and image data 2.

The image of the secondary target 271 a just before being irradiatedwith the second prepulse laser beam 33 d may be, for example, the imageas shown in FIG. 46.

FIG. 47 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 43, where the image of the tertiary target271 b just before being irradiated with the main pulse laser beam 33 ais measured.

With the time chart shown in FIG. 47, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texd in the one-shot circuit 835 inadvance. The shutter opening time Texd may be a period of time which isnecessary and sufficient to capture the image of the tertiary target 271b.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdsd in the delay circuit 833. When the image of the tertiary target271 b just before being irradiated with the main pulse laser beam 33 ais captured, the imaging timing of the imaging part 422 and the imagingpart 432 may be defined as follows. A summed value “Tdsd+Texd” of thedelay time Tdsd that defines the output timing of the shutter openingsignal and the shutter opening time Texd may be equal to or smaller thana value “delay time Tdlm+time α2” that defines the irradiation timing ofthe main pulse laser beam 33 a.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIG. 46.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 47, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831 in the same way as the case shown in FIG. 46.

Then, as shown in FIG. 47, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement, in the same way asthe case shown in FIG. 46.

Then, as shown in FIG. 47, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834 in the same way as the case shown in FIG. 46. When theenable signal is inputted from the AND circuit 831 to the delay circuit833, the delay circuit 833 may output the enable signal to the one-shotcircuit 835 at the timing delayed by the delay time Tdsd. When theenable signal is inputted from the AND circuit 831 to the delay circuit834, the delay circuit 834 may output the enable signal to the one-shotcircuit 836 at the timing delayed by the delay time Tdi in the same wayas the case shown in FIG. 46.

Then, as shown in FIG. 47, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals to the image sensor 422 a and the image sensor 432 a inthe same way as the case shown in FIG. 46.

Then, as shown in FIG. 47, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the first prepulse laser device 3 c at the timing delayed bythe delay time Tdlp1 in the same way as the case shown in FIG. 46. Inaddition, when the droplet detection signal is inputted to the delaycircuit 82, the delay circuit 82 may output a trigger signal to thesecond prepulse laser device 3 d at the timing delayed by the delay timeTdlp2 in the same way as the case shown in FIG. 46. Moreover, when thedroplet detection signal is inputted to the delay circuit 82, the delaycircuit 82 may output a trigger signal to the main pulse laser device 3a at the timing delayed by the delay time Tdlm in the same way as thecase shown in FIG. 46.

Then, as shown in FIG. 47, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texd tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals, in the same way as the case shown in FIG. 46. The shutter 422 dand the shutter 432 d may be open from when the shutter opening signalsare inputted until the shutter opening time Texd has elapsed.

Then, as shown in FIG. 47, when the output signal from the one-shotcircuit 835 and the gate signal are inputted to the AND circuit 832, theAND circuit 832 may output lighting signals each having the pulse widthof the shutter opening time Texd to the light source 421 a and the lightsource 431 a, in the same way as the case shown in FIG. 46. The gatesignal may be outputted from the shooting controller 81 to the ANDcircuit 832 before the one-shot circuit 835 outputs the output signal tothe AND circuit 832, in the same way as the case shown in FIG. 46. Thelight source 421 a and the light source 431 a may emit pulsed light fromwhen the lighting signals are inputted until the shutter opening timeTexd has elapsed.

Then, as shown in FIG. 47, plasma light may be emitted after the shutteropening time Texd has elapsed, from the tertiary target 271 b irradiatedwith the main pulse laser beam 33 a. The imaging part 422 and theimaging part 432 may capture the image of the tertiary target 271 b justbefore being irradiated with the main pulse laser beam 33 a.

Then, as shown in FIG. 47, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the tertiary target 271 b just before being irradiatedwith the main pulse laser beam 33 a. The shooting controller 81 maycalculate the measurement position Cs2(Xs2, Ys2, Zs2) of the tertiarytarget 271 b, based on the acquired image data 1 and image data 2.

The image of the tertiary target 271 b just before being irradiated withthe main pulse laser beam 33 a may be, for example, the image as shownin FIG. 47.

FIG. 48 is a time chart for the image measurement performed by thecontroller 8 shown in FIG. 43, where the image of the plasma lightemitted from the tertiary target 271 b just after being irradiated withthe main pulse laser beam 33 a is measured.

With the time chart shown in FIG. 48, the shooting controller 81 may setthe shutter opening time Tex as Tex=Texe in the one-shot circuit 835 inadvance. The shutter opening time Texe may be a period of time which isnecessary and sufficient to capture the image of the plasma light.

Moreover, the shooting controller 81 may set the delay time Tds asTds=Tdse in the delay circuit 833. When the image of the plasma lightemitted from the tertiary target 271 b just after being irradiated withthe main pulse laser beam 33 a is captured, the imaging timing of theimaging part 422 and the imaging part 432 may be defined as follows. Asummed value “Tdse+Texe” of the delay time Tdse that defines the outputtiming of the shutter opening signal and the shutter opening time Texemay be greater than a value “delay time Tdlm+time α2” that defines theirradiation timing of the main pulse laser beam 33 a.

The delay time Tdi of the delay circuit 834 and the exposure time Tr ofthe one-shot circuit 836 may be set in advance as the initial setting atstartup in the same way as the case shown in FIG. 47.

The controller 8 may control the output timings of various signals forthe image measurement as follows, based on droplet detection signalsoutputted from the droplet detector 41.

As shown in FIG. 48, the shooting controller 81 may output the dropletdetection signals directly to the delay circuit 82 and the AND circuit831 in the same way as the case shown in FIG. 47.

Then, as shown in FIG. 48, the shooting controller 81 may output animage measurement signal to the AND circuit 831 when the shootingcontroller 81 causes the image measurement unit 42 and the imagemeasurement unit 43 to perform the image measurement, in the same way asthe case shown in FIG. 47.

Then, as shown in FIG. 48, when the image measurement signal and thedroplet detection signal are inputted to the AND circuit 831, the ANDcircuit 831 may output enable signals to the delay circuit 833 and thedelay circuit 834 in the same way as the case shown in FIG. 47. When theenable signal is inputted from the AND circuit 831 to the delay circuit833, the delay circuit 833 may output the enable signal to the one-shotcircuit 835 at the timing delayed by the delay time Tdse. When theenable signal is inputted from the AND circuit 831 to the delay circuit834, the delay circuit 834 may output the enable signal to the one-shotcircuit 836 at the timing delayed by the delay time Tdi in the same wayas the case shown in FIG. 47.

Then, as shown in FIG. 48, when the enable signal is inputted to theone-shot circuit 836, the one-shot circuit 836 may output image sensorexposure signals to the image sensor 422 a and the image sensor 432 a inthe same way as the case shown in FIG. 47.

Then, as shown in FIG. 48, when the droplet detection signal is inputtedto the delay circuit 82, the delay circuit 82 may output a triggersignal to the first prepulse laser device 3 c at the timing delayed bythe delay time Tdlp1 in the same way as the case shown in FIG. 47. Inaddition, when the droplet detection signal is inputted to the delaycircuit 82, the delay circuit 82 may output a trigger signal to thesecond prepulse laser device 3 d at the timing delayed by the delay timeTdlp2 in the same way as the case shown in FIG. 47. Moreover, when thedroplet detection signal is inputted to the delay circuit 82, the delaycircuit 82 may output a trigger signal to the main pulse laser device 3a at the timing delayed by the delay time Tdlm in the same way as thecase shown in FIG. 47.

Then, as shown in FIG. 48, when the enable signal is inputted to theone-shot circuit 835, the one-shot circuit 835 may output the outputsignals each having the pulse width of the shutter opening time Texe tothe shutter 422 d, the shutter 432 d, and the AND circuit 832. Among theoutput signals from the one-shot circuit 835, the signals inputted tothe shutter 422 d and the shutter 432 d may function as shutter openingsignals, in the same way as the case shown in FIG. 47. The shutter 422 dand the shutter 432 d may be open from when the shutter opening signalsare inputted until the shutter opening time Texe has elapsed.

Then, as shown in FIG. 48, the AND circuit 832 may not output lightingsignals to the light source 421 a and the light source 431 a. When theimage of the plasma light is captured, the shooting controller 81 maynot output a gate signal to the AND circuit 832.

Then, as shown in FIG. 48, plasma light may be emitted from the tertiarytarget 271 b irradiated with the main pulse laser beam 33 a, during theshutter opening time Texe. This plasma light may contain the EUV light251. The imaging part 422 and the imaging part 432 may capture the imageof the plasma light emitted from the tertiary target 271 b just afterbeing irradiated with the main pulse laser beam 33 a.

Then, as shown in FIG. 48, the image sensor 422 a and the image sensor432 a may generate the image data 1 and the image data 2 and output thedata to the shooting controller 81, after the exposure time Tr haselapsed. The shooting controller 81 may acquire the image data 1 and theimage data 2 of the plasma light emitted from the tertiary target 271 bjust after being irradiated with the main pulse laser beam 33 a. Theshooting controller 81 may calculate the measurement position Cpm(Xpm,Ypm, Zpm) of the plasma light, based on the acquired image data 1 andimage data 2.

The image of the plasma light emitted from the tertiary target 271 bjust after being irradiated with the main pulse laser beam 33 a may be,for example, the image as shown in FIG. 48.

Next, a process for the shooting control of the shooting system usingthe EUV light generation apparatus 1 according to Embodiment 4 will bedescribed. The process for the shooing control performed by the shootingcontroller 81 according to Embodiment 4 may be the same as the processfor the shooting control including the subroutines performed by theshooting controller 81 according to Embodiment 3, shown in FIGS. 30 to41C.

First, the shooting controller 81 according to Embodiment 4 may read thetarget position Ppt of the plasma light. The target position Ppt(Xpt,Ypt, Zpt) of the plasma light may be a target value for the centerposition of the plasma light emitted from the tertiary target 271 b justafter being irradiated with the main pulse laser beam 33 a in the plasmageneration region 25.

Next, the shooting controller 81 may calculate the target position Pdtof the droplet 271, the target position Pst1 of the secondary target 271a, and the target position Pst2 of the tertiary target 271 b, based onthe target position Ppt of the plasma light. The target positionPdt(Xdt, Ydt, Zdt) of the droplet 271 may be a target value for thecenter position of the droplet 271 just before being irradiated with thefirst prepulse laser beam 33 c in the plasma generation region 25. Thetarget position Pst1 (Xst1, Yst1, Zst1) of the secondary target 271 amay be a target value for the center position of the secondary target271 a just before being irradiated with the second prepulse laser beam33 d in the plasma generation region 25. The target position Pst2 (Xst2,Yst2, Zst2) of the tertiary target 271 b may be a target value for thecenter position of the tertiary target 271 b just before beingirradiated with the main pulse laser beam 33 a in the plasma generationregion 25.

Next, the shooting controller 81 may set the target position Pdt of thedroplet 271, and the target focused positions of the first prepulselaser beam 33 c, the second prepulse laser beam 33 d, and the main pulselaser beam 33 a. The shooting controller 81 may set the delay time Tds,the delay time Tdl, and the biaxial stage 74 in order to supply thedroplet 271 to the target position Pdt of the droplet 271. The shootingcontroller 81 may set the biaxial stage 227 and the wavefront adjustmentunit 38 in order to focus the first prepulse laser beam 33 c on thetarget position Pdt of the droplet 271.

The shooting controller 81 may set the wavefront adjustment unit 39 inorder to focus the second prepulse laser beam 33 d on the targetposition Pst1 of the secondary target 271 a. As described above, whenthe second prepulse laser beam 33 d and the first prepulse laser beam 33c which are approximately coaxial with one another are irradiated, theX-coordinate of the target position Pst1 and the X-coordinate of thetarget position Pdt shown in FIG. 44A to 44C may be the same as eachother; the Y-coordinate of the target position Pst1 and the Y-coordinateof the target position Pdt shown in FIG. 44A to 44C may be the same aseach other. In this case, the X-coordinates and the Y-coordinates of thetarget positions on which the second prepulse laser beam 33 d and thefirst prepulse laser beam 33 c should be focused may be adjusted by thebiaxial stage 227 at the same time. In addition, the Z-coordinates ofthe target positions on which the second prepulse laser beam 33 d andthe first prepulse laser beam 33 c should be focused may be adjusted bythe wavefront adjustment unit 39 and the wavefront adjustment unit 38,respectively. On the other hand, when the second prepulse laser beam 33d and the first prepulse laser beam 33 c which are not approximatelycoaxial with one another are irradiated, the X-coordinate of the targetposition Pst1 and the X-coordinate of the target position Pdt shown inFIG. 44A to 44C may not be the same as each other; the Y-coordinate ofthe target position Pst1 and the Y-coordinate of the target position Pdtshown in FIG. 44A to 44C may not be the same as each other. In thiscase, a prepulse beam path adjustment mechanism (not shown) may beprovided on the optical path of the first prepulse laser beam 31 c orthe second prepulse laser beam 31 d shown in FIG. 43. This prepulse beampath adjustment mechanism may be provided on a position from the firstprepulse laser device 3 c or the second prepulse laser device 3 d to thebeam combiner 348. The prepulse beam path adjustment mechanism may beformed with optical elements such as a mirror and a lens. Theconfiguration of the prepulse beam path adjustment mechanism may be acombination of, for example, the high-reflection mirror 342 and the tiltstage 353.

The shooting controller 81 may set the tilt stage 353 and the wavefrontadjustment unit 36 to focus the main pulse laser beam 33 a on the targetposition Pst2 of the tertiary target 271 b.

Next, the shooting controller 81 may control the position of the droplet271 outputted from the target supply part 26. To be more specific, theshooting controller 81 may perform the following process until theposition of the droplet 271 just before being irradiated with the firstprepulse laser beam 33 c in the plasma generation region 25 is withinthe allowable range. The shooting controller 81 may cause the imagemeasurement unit 42 and the image measurement unit 43 to measure theimage of the droplet 271 just before being irradiated with the firstprepulse laser beam 33 c in the plasma generation region 25. Then, theshooting controller 81 may calculate the measurement position Cd of thedroplet 271 based on the acquired image data. Then, the shootingcontroller 81 may appropriately modify and set the delay time Tdlp1 andcontrol the operation of the biaxial stage 74, based on the calculatedmeasurement position Cd of the droplet 271. Moreover, the shootingcontroller 81 may appropriately modify and set the delay time Tdsc1. Bythis means, the shooting controller 81 can control the position of thedroplet 271 based on the image of the droplet 271.

Next, the shooting controller 81 may control the position of thesecondary target 271 a. To be more specific, the shooting controller 81may perform the following process until the position of the secondarytarget 271 a just before being irradiated with the second prepulse laserbeam 33 d in the plasma generation region 25 is within the allowablerange. The shooting controller 81 may cause the image measurement unit42 and the image measurement unit 43 to measure the image of thesecondary target 271 a just before being irradiated with the secondprepulse laser beam 33 d in the plasma generation region 25. Then, theshooting controller 81 may calculate the measurement position Cs1 of thesecondary target 271 a based on the acquired image data. Then, theshooting controller 81 may appropriately modify and set the delay timeTdlp2 based on the calculated measurement position Cs1 of the secondarytarget 271 a. In addition, the shooting controller 81 may control theoperations of the biaxial stage 227 and the wavefront adjustment unit38, based on the calculated measurement position Cs1 of the secondarytarget 271 a. Moreover, the shooting controller 81 may appropriatelymodify and set the delay time Tdsc2, and control the operation of thebiaxial stage 74. By this means, the shooting controller 81 can controlthe focused position of the first prepulse laser beam 33 c, based on theimage of the secondary target 271 a.

Next, the shooting controller 81 may control the position of thetertiary target 271 b. To be more specific, the shooting controller 81may perform the following process until the position of the tertiarytarget 271 b just before being irradiated with the main pulse laser beam33 a in the plasma generation region 25 is within the allowable range.The shooting controller 81 may cause the image measurement unit 42 andthe image measurement unit 43 to measure the image of the tertiarytarget 271 b just before being irradiated with the main pulse laser beam33 a in the plasma generation region 25. Then, the shooting controller81 may calculate the measurement position Cs2 of the tertiary target 271b based on the acquired image data. Then, the shooting controller 81 mayappropriately modify and set the delay time Tdlm, based on thecalculated measurement position Cs2 of the tertiary target 271 b. Inaddition, the shooting controller 81 may control the operation of thewavefront adjustment unit 39 based on the calculated measurementposition Cs2 of the tertiary target 271 b. Moreover, when the secondprepulse laser beam 33 d and the first prepulse laser beam 33 c whichare not approximately coaxial with one another are irradiated, theshooting controller 81 may control the operation of the prepulse beampath adjustment mechanism (not shown). In addition, the shootingcontroller 81 may appropriately modify and set the delay time Tdsd andcontrol the operation of the biaxial stage 74. Moreover, the shootingcontroller 81 may control the operations of the biaxial stage 227 andthe wavefront adjustment unit 38. By this means, the shooting controller81 can control the focused position of the second prepulse laser beam 33d, based on the image of the tertiary target 271 b.

Next, the shooting controller 81 may control the focused position of themain pulse laser beam 33 a. To be more specific, the shooting controller81 may perform the following process until the position of the plasmalight emitted from the tertiary target 271 b just after being irradiatedwith the main pulse laser beam 33 a in the plasma generation region 25is within the allowable range. The shooting controller 81 may cause theimage measurement unit 42 and the image measurement unit 43 to measurethe image of the plasma light emitted from the tertiary target 271 bjust after being irradiated with the main pulse laser beam 33 a in theplasma generation region 25. Then, the shooting controller 81 maycalculate the measurement position Cpm of the plasma light based on theacquired image data. Then, the shooting controller 81 may control theoperations of the tilt stage 353 and the wavefront adjustment unit 36,based on the calculated measurement position Cpm of the plasma light. Inaddition, the shooting controller 81 may appropriately modify and setthe delay time Tdlm, appropriately modify and set the delay time Tdse,and control the operation of the biaxial stage 74, based on thecalculated measurement position Cpm of the plasma light. Moreover, theshooting controller 81 may control the operations of the biaxial stage227, the wavefront adjustment unit 38, and the wavefront adjustment unit39, based on the calculated measurement position Cpm of the plasmalight. By this means, the shooting controller 81 can control the focusedposition of the main pulse laser beam 33 a, based on the image of theplasma light.

With the above-described process for the shooting control, it ispossible to substantially match the measurement position Cpm of theplasma light emitted from the tertiary target 271 b just after beingirradiated with the main pulse laser beam 33 a in the plasma generationregion 25 with the target position Ppt of the plasma light. Here, thedetails of the process for the shooting control performed by theshooting controller 81 according to Embodiment 4 may be the same asthose of the process performed by the shooting controller 81 accordingto the Embodiment 3 described with reference to FIGS. 31A to 41C.

8.3 Effect

The EUV light generation apparatus 1 according to Embodiment 4 canprecisely control the positions of the droplet 271, the secondary target271 a, and the tertiary target 271 b in the plasma generation region 25.Moreover, the EUV light generation apparatus 1 can precisely control thefocused positions of the first prepulse laser beam 33 c, the secondprepulse laser beam 33 d, and the main pulse laser beam 33 a. Therefore,the EUV light generation apparatus 1 according to Embodiment 4 cansubstantially match the position of the droplet 271 with the focusedposition of the first prepulse laser beam 33 c, and consequentlygenerate the secondary target 271 a that can efficiently generate plasmalight. In addition, the EUV light generation apparatus 1 cansubstantially match the position of the secondary target 271 a with thefocused position of the second prepulse laser beam 33 d, andconsequently generate the tertiary target 271 b that can moreefficiently generate plasma light. Moreover, the EUV light generationapparatus 1 can substantially match the position of the tertiary target271 b with the focused position of the main pulse laser beam 33 a, andtherefore efficiently generate plasma light. Consequently, the EUV lightgeneration apparatus 1 according to Embodiment 4 can generate the EUVlight 252 more efficiently than the EUV light generation apparatus 1according to Embodiment 3. Moreover, the EUV light generation apparatus1 according to Embodiment 4 can substantially match the position of theplasma light actually emitted in the plasma generation region 25 withthe target position of the plasma light determined according to acommand from the exposure apparatus 6. Consequently, the EUV lightgeneration apparatus 1 can stably output the EUV light 252 to theexposure apparatus 6.

9. Image Measurement Unit of the EUV Light Generation ApparatusAccording to Embodiment 5

9.1 Configuration

Now, the image measurement units 42 and 43 of the EUV light generationapparatus 1 according to Embodiment 5 will be described with referenceto FIGS. 49 to 51B. Here, the configuration of the image measurementunit 42 and the image measurement unit 43 of the EUV light generationapparatus 1 according to Embodiment 5 may be different from that of theimage measurement unit 42 and the image measurement unit 43 of the EUVlight generation apparatus 1 according to Embodiment 4 shown in FIG. 43.The configuration of the image measurement unit 42 and the imagemeasurement unit 43 of the EUV light generation apparatus 1 according toEmbodiment 5, which is the same as that of the image measurement unit 42and the image measurement unit 43 of the EUV light generation apparatus1 according to Embodiment 4 shown in FIG. 43, will not be describedagain here.

FIG. 49 is a drawing showing the configuration of the image measurementunit 42 and the image measurement unit 43 of the EUV light generationapparatus 1 according to Embodiment 5. In FIG. 49, an X′ axis and a Z′axis may be coordinate axes obtained by rotating the X axis and the Zaxis about the Y axis by a predetermined angle.

The image measurement unit 42 shown in FIG. 49 may capture the image ofthe imaging region 25 a in the X′ direction and measure the images ofthe droplet 271, the secondary target 271 a, the tertiary target 271 band the plasma light. Here, the imaging region 25 a may be formed tocontain the plasma generation region 25. The image measurement unit 42may include the light source part 421 and the imaging part 422. Thedirection in which the light source part 421 faces the imaging part 422may be approximately perpendicular to the target traveling path 272. Thedirection in which the light source part 421 faces the imaging part 422may be the X′ direction. The light source part 421 and the imaging part422 may be placed in a plane A which is approximately parallel to anX′-Z′ plane and intersects the imaging region 25 a. When a specificdroplet 271 is placed in the ideal position in the plasma generationregion 25, the plane A may intersect the diameter of the droplet 271.

A line sensor 422 e including light receiving elements arranged in onedimension may be used in the imaging part 422, instead of the imagesensor 422 a shown in FIG. 43. The imaging part 422 may include the linesensor 422 e, the transfer optical system 422 b, the window 422 c andthe shutter 422 d. Here, the transfer optical system 422 b, the window422 c and the shutter 422 d are not shown in FIG. 49.

The transfer optical system 422 b may transfer an image of the imagingregion 25 a including the intersection of the plane A and the targettraveling path 272 onto the light receiving elements of the line sensor422 e and form the image thereon. The transfer optical system 422 b maytransfer an image of the light, of the imaging region 25 a, havingexited the light source 421 and passing through the plane A onto thelight receiving elements of the line sensor 422 e and form the imagethereon.

The line sensor 422 e may capture the image of the light transferred andformed by the transfer optical system 422 b. The light receivingelements of the line sensor 422 e may be arranged in the directionapproximately perpendicular to the direction in which the light sourcepart 421 faces the imaging part 422. The light receiving elements of theline sensor 422 e may intersect the plane A and be arrangedapproximately parallel to each other. The channels of the line sensor422 e may be arranged to correspond to the respective light receivingelements of the line sensor 422 e. The line sensor 422 e may generate adetection signal according to the optical intensity of the capturedimage of the light. The line sensor 422 e may measure the parameters ofthe droplet 271 based on the detection signal, and output the measuredresult to the shooting controller 81.

The image measurement unit 43 shown in FIG. 49 may capture the image ofthe imaging region 25 a in the Z′ direction, and measure the images ofthe droplet 271, the secondary target 271 a, the tertiary target 271 b,and the plasma light. The image measurement unit 43 may include thelight source part 431 and the imaging part 432. The direction in whichthe light source part 431 faces the imaging part 432 may beapproximately perpendicular to the target traveling path 272. Thedirection in which the light source part 431 faces the imaging part 432may be the Z′ direction. The light source part 431 and the imaging part432 may be placed in a plane B which is approximately parallel to theX′-Z′ plane and intersects the imaging region 25 a. The plane B may beapproximately parallel to the plane A, and placed in a position which isa predetermined distance apart from the plane A in the +Y direction.When a specific droplet 271 is placed in the ideal position in theplasma generation region 25, the plane B may intersect a portion of thedroplet 271 which is different from the portion intersecting the planeA.

A line sensor 432 e including light receiving elements arranged in onedimension may be used in the imaging part 432, instead of the imagesensor 432 a shown in FIG. 43. The imaging part 432 may include the linesensor 432 e, the transfer optical system 432 b, the window 432 c andthe shutter 432 d. Here, the transfer optical system 432 b, the window432 c and the shutter 432 d are not shown in FIG. 49.

The transfer optical system 432 b may transfer an image of the imagingregion 25 a including the intersection of the plane B and the targettraveling path 272 onto the light receiving elements of the line sensor432 e and form the image thereon. The transfer optical system 432 b maytransfer an image of the light, of the imaging region 25 a, havingexited the light source part 431 and passing through the plane B ontothe light receiving elements of the line sensor 432 e and form the imagethereon.

The line sensor 432 e may capture the image of the light transferred andformed by the transfer optical system 432 b. The light receivingelements of the line sensor 432 e may be arranged in the directionapproximately perpendicular to the direction in which the light sourcepart 431 faces the imaging part 432. The light receiving elements of theline sensor 432 e may intersect the plane B and be arrangedapproximately parallel to each other. The channels of the line sensor432 e may be arranged to correspond to the respective light receivingelements of the line sensor 432 e. The line sensor 432 e may generate adetection signal according to the optical intensity of the capturedimage of the light, and output the detection signal to the shootingcontroller 81. The shooting controller 81 may measure the parameters ofthe droplet 271 based on the detection signal.

The line sensor 422 e and the line sensor 432 e may capture the image ofthe droplet 271 reaching the plasma generation region 25 at the sametime. The imaging timing of the line sensor 422 e and the line sensor432 e may be the timing at which the diameter of the droplet 271intersects the plane A. Each of the line sensor 422 e and the linesensor 432 e may perform an imaging operation once for one droplet 271.The other configurations of the image measurement unit 42 and the imagemeasurement unit 43 may be the same as those of the image measurementunit 42 and the image measurement unit 43 shown in FIG. 43.

9.2 Operation

Now, the operations of the image measurement unit 42 and the imagemeasurement unit 43 of the EUV light generation apparatus 1 according toEmbodiment 5 will be described with reference to FIGS. 50A to 51B. FIG.50A shows a result of the measurement by the line sensor 422 e when thedroplet 271 is placed in a proper position in the plasma generationregion 25. FIG. 50B shows a result of the measurement by the line sensor432 e when the droplet 271 is placed in the proper position in theplasma generation region 25. FIG. 51A shows a result of the measurementby the line sensor 422 e when the droplet 271 is placed out of theproper position in the plasma generation region 25. FIG. 51B shows aresult of the measurement by the line sensor 432 e when the droplet 271is placed out of the proper position in the plasma generation region 25.Here, the vertical axis of FIG. 50A represents the intensity of thedetection signal generated by the line sensor 422 e. The horizontal axisof FIG. 50A represents channel numbers sequentially assigned to thechannels of the line sensor 422 e. The vertical axis of FIG. 50Brepresents the intensity of the detection signal generated by the linesensor 432 e. The horizontal axis of FIG. 50B represents channel numberssequentially assigned to the channels of the line sensor 432 e. Thevertical axis and the horizontal axis shown in FIGS. 51A and 51B are thesame as those shown in FIGS. 50A and 50B.

When the droplet 271 reaches the plasma generation region 25, the lightemitted from the light source part 421 and the light source part 431 isblocked by the droplet 271, and therefore the imaging part 422 and theimaging part 432 may capture the image of the shadow of the droplet 271.Then, the optical intensity of the image of the light blocked by thedroplet 271 may be significantly reduced as compared to when the droplet271 has not reached the plasma generation region 25. Therefore, when thedroplet 271 reaches the plasma generation region 25, the intensity ofthe detection signal generated by each of the line sensor 422 e and theline sensor 432 e may be significantly reduced as compared to when thedroplet 271 has not reached the plasma generation region 25.

First, the line sensor 422 e and the line sensor 432 e may measure theposition of the droplet in the X′-Z′ plane as a reference position, whenthe droplet is placed in the proper position as shown in FIGS. 50A and50B. To be more specific, the line sensor 422 e and the line sensor 432e may specify a channel number Na and a channel number Nb with which theintensities of the respective detection signals are lowest. Then, theline sensor 422 e and the line sensor 432 e may measure the specifiedchannel number Na and channel number Nb as the reference position of thedroplet 271.

Next, the line sensor 422 e and the line sensor 432 e may measure thelengths of the droplet 271 in the Z′ direction and the X′ direction, asreference lengths, when the droplet 271 is placed in the properposition. To be more specific, the line sensor 422 e and the line sensor432 e may calculate the number of channels (Na2−Na1) and the number ofchannels (Nb2−Nb1) with which the intensities of the detection signalsare lower than a threshold value A and a threshold value B,respectively. Then, the line sensor 422 e and the line sensor 432 e maymeasure the number of channels (Na2−Na1) and the number of channels(Nb2−Nb1) as a reference length D (=Na2−Na1) and a reference length d(=Nb2−Nb1) of the droplet 271, respectively.

Next, the line sensor 422 e and the line sensor 432 e may measure theamount of the shifting of the droplet 271 from the reference position inthe Z′ direction and the X′ direction when the droplet 271 is placed outof the proper position as shown in FIGS. 51A and 51B. To be morespecific, the line sensor 422 e and the line sensor 432 e may specify achannel number Na′ and a channel number Nb′ with which the intensitiesof the respective detection signals are lowest. Then, the line sensor422 e and the line sensor 432 e may calculate the differences (Na′−Na)and (Nb′−Nb) in the specified channel number Na′ and channel number Nb′from the channel number Na and the channel number Nb at the referenceposition, respectively. Then, the line sensor 422 e and the line sensor432 e may measure the calculated differences as an amount of shiftingΔZ′ (=Na′−Na) and an amount of shifting ΔX′(=Nb′−Nb) from the referenceposition in the Z′ direction and the X′ direction, respectively. Here,by the coordinate transformation of ΔZ′ and ΔX′, it is possible tocalculate an amount of shifting ΔZ and an amount of shifting ΔX in the Zdirection and the X direction, respectively. Moreover, the channelnumber Na may be calculated as a channel number at the midpoint betweenNa1 and Na2. The channel numbers Na′, Nb, and Nb′ may be calculated inthe same way as the channel number Na.

Next, the line sensor 422 e and the line sensor 432 e may measure theobserved length of the droplet 271 in the Z′ direction and the X′direction when the droplet 271 is placed out of the proper position. Tobe more specific, the line sensor 422 e and the line sensor 432 e maycalculate the number of channels (Na2′−Na1′) and the number of channels(Nb2′−Nb1′) with which the intensities of the detection signals arelower than the threshold value A and the threshold value B,respectively. Then, the line sensor 422 e and the line sensor 432 e maymeasure the number of channels (Na2′−Na1′) and the number of channels(Nb2′−Nb1′) as an observed length D′ (=Na2′−Na1′) and an observed lengthd′ (=Nb2′−Nb1′), respectively.

Next, the line sensor 422 e and the line sensor 432 e may measure theamount of the shifting of the droplet 271 in the Y direction when thedroplet 271 is placed out of the proper position as shown in FIGS. 51Aand 51B. To be more specific, the line sensor 422 e and the line sensor432 e may calculate the amount of shifting |ΔY| of the droplet 271 inthe Y direction according to the following equation.|ΔY|=D·cos(sin⁻¹(D′/D))

Next, with respect to the Y direction, the line sensor 422 e and theline sensor 432 e may specify the direction in which the droplet 271 isshifted, by calculating (d′−d). To be more specific, when the calculatedresult is (d′−d)>0, the line sensor 422 e and the line sensor 432 e maydetermine that the droplet 271 is shifted from the plane B in the +Ydirection. On the other hand, when the calculated result is (d′−d)<0,the line sensor 422 e and the line sensor 432 e may determine that thedroplet 271 is shifted from the plane B in the −Y direction.

As described above, a case has been described with reference to FIGS. 49to 51B where the droplet 271 is the target 27 to be measured by theimage measurement unit 42 and the image measurement unit 43 of the EUVlight generation apparatus 1 according to Embodiment 5. However, thetarget 27 to be measured by the image measurement unit 42 and the imagemeasurement unit 43 of the EUV light generation apparatus 1 according toEmbodiment 5 may be the secondary target 271 a, the tertiary target 271b and the plasma light. In particular, the shape of the secondary target271 a and the shape of the tertiary target 271 b may often beaxisymmetric. Therefore, when the secondary target 271 a and thetertiary target 271 b are measurement targets, the line sensor 422 e andthe line sensor 432 e may be configured such that the symmetric axes ofthe secondary target 271 a and the tertiary target 271 b can fall withinthe plane A. Moreover, the imaging timing of the line sensor 422 e andthe line sensor 432 e may be the timing at which the symmetric axes ofthe secondary target 271 a and the tertiary target 271 b fall within theplane A. In addition, the optical intensity of the plasma light may behigher than that of the light emitted from the light source part 421 andthe light source part 431, and therefore the intensity of the detectionsignal generated by each of the line sensor 422 e and the line sensor432 e may be increased. Therefore, when the measurement target is theplasma light, the line sensor 422 e and the line sensor 432 e mayspecify the channel numbers with which the intensities of the detectionsignals are highest as Na and Nb, respectively, and measure them as thereference position of the plasma light. Here, the amount of the shiftingof the target 27 in the Y direction may be measured by using a pluralityof data obtained by capturing the images of one target 27 at differenttimings. In this case, the line sensor 422 e and the line sensor 432 emay be placed on approximately the same plane.

9.3 Effect

The EUV light generation apparatus 1 according to Embodiment 5 canmeasure the parameters of the droplet 271, the secondary target 271 a,the tertiary target 271 b and the plasma light, by using the line sensor422 e and the line sensor 432 e. Therefore, the EUV light generationapparatus 1 according to Embodiment 5 can measure the parameters of thedroplet 271, the secondary target 271 a, the tertiary target 271 b andthe plasma light at a lower cost and a higher speed than the EUV lightgeneration apparatus 1 according to Embodiment 4.

10. Others

10.1 Hardware Environment of Each Controller.

A person skilled in the art would understand that the subject mattersdisclosed herein can be implemented by combining a general purposecomputer or a programmable controller with a program module or asoftware application. In general, the program module includes routines,programs, components and data structures which can execute the processesdescribed herein.

FIG. 52 is a block diagram showing an exemplary hardware environment inwhich various aspects of the subject matters disclosed herein can beimplemented. An exemplary hardware environment 100 shown in FIG. 52 mayinclude a processing unit 1000, a storage unit 1005, a user interface1010, a parallel I/O controller 1020, a serial I/O controller 1030, andan A/D, D/A converter 1040, but the configuration of the hardwareenvironment 100 is not limited to this.

The processing unit 1000 may include a central processing unit (CPU)1001, a memory 1002, a timer 1003, and a graphics processing unit (GPU)1004. The memory 1002 may include a random access memory (RAM) and aread only memory (ROM). The CPU 1001 may be any of commerciallyavailable processors. A dual microprocessor or another multiprocessorarchitecture may be used as the CPU 1001.

The components shown in FIG. 52 may be interconnected with each other toperform the processes described herein.

During its operation, the processing unit 1000 may read and execute theprogram stored in the storage unit 1005, read data together with theprogram from the storage unit 1005, and write the data to the storageunit 1005. The CPU 1001 may execute the program read from the storageunit 1005. The memory 1002 may be a work area in which the programexecuted by the CPU 1001 and the data used in the operation of the CPU1001 are temporarily stored. The timer 1003 may measure a time intervaland output the result of the measurement to the CPU 1001 according tothe execution of the program. The GPU 1004 may process image dataaccording to the program read from the storage unit 1005, and output theresult of the process to the CPU 1001.

The parallel I/O controller 1020 may be connected to parallel I/Odevices that can communicate with the processing unit 1000, such as theexposure apparatus controller 61, the EUV light generation controller 5,the laser beam direction control unit 34, the shooting controller 81,the delay circuit 82, the image measurement control circuit 83, theimage sensor 422 a, and the image sensor 432 a. The parallel I/Ocontroller 1020 may control the communication between the processingunit 1000 and those parallel I/O devices. The serial I/O controller 1030may be connected to serial I/O devices that can communicate with theprocessing unit 1000, such as the heater power source 712, thepiezoelectric power source 732, the pressure regulator 721, the lightsource 411 a, the light source 421 a, the light source 431 a, thebiaxial stage 74, the triaxial stage 226, and the biaxial stage 227. Theserial I/O controller 1030 may control the communication between theprocessing unit 1000 and those serial I/O devices. The A/D, D/Aconverter 1040 may be connected to analog devices such as thetemperature sensor, the pressure sensor, various sensors for a vacuumgauge, the target sensor 4, the optical sensor 412 a, the shutter 422 d,the shutter 432 d, the line sensor 422 e, and the line sensor 432 e, viaanalog ports, may control the communication between the processing unit1000 and those analog devices, and may perform A/D, D/A conversion ofthe contents of the communication.

The user interface 1010 may present the progress of the program executedby the processing unit 1000 to an operator, in order to allow theoperator to command the processing unit 1000 to stop the program and toexecute an interruption routine.

The exemplary hardware environment 100 may be applicable to the exposureapparatus controller 61, the EUV light generation controller 5, thelaser beam direction control unit 34, and the shooting controller 81 inthe present disclosure. A person skilled in the art would understandthat those controllers may be realized in a distributed computingenvironment, that is, an environment in which tasks are performed byprocessing units connected to each other via a communication network. Inthis disclosure, the exposure apparatus controller 61, the EUV lightgeneration controller 5, the laser beam direction control unit 34, andthe shooting controller 81 may be connected to each other via acommunication network such as Ethernet or Internet. In the distributedcomputing environment, the program module may be stored in both of alocal memory storage device and a remote memory storage device.

10.2 Configuration of Shutters

The shutter 422 d of the imaging part 422 may have the configurationshown in FIG. 53. The shutter 432 d of the imaging part 432 may have thesame configuration as that of the shutter 422 d.

The shutter 422 d shown in FIG. 53 may be an image intensifier by usinga microchannel plate. The image intensifier may be a vacuum tube thatcan produce an optical image, by introducing incident light; multiplyingphotoelectrons emitted from a photoelectric surface; converting theelectrons into light by a fluorescent screen; and emitting the light toform the image. The image intensifier shown in FIG. 53 may be providedon the light receiving surface of the image sensor 422 a. This imageintensifier may include an entrance window, a photoelectric surface, amicrochannel plate, a fluorescent screen, and an output window. Here,“p” represents a photon and “e” represents an electron in FIG. 53.

The entrance window may introduce incident light onto the photoelectricsurface. The photoelectric surface may convert the incident light intophotoelectrons and emit the photoelectrons to the multichannel plate.The multichannel plate may be structured by tying a number of channelstogether, which allow the photoelectrons to pass therethrough. When aphotoelectron passing through the channels collides against an innerwall of the channels, the multichannel plate may emit secondaryelectrons. By this means, the multichannel plate may multiply thephotoelectron emitted from the photoelectric surface and emit thesecondary electrons to the fluorescent screen. The fluorescent screenmay convert the electrons having been multiplied by the multichannelplate into light, and guide the light to the output window. The outputwindow may be adjacent to the light receiving surface of the imagesensor 422 a. The output window may output the light from thefluorescent screen to the image sensor 422 a as exit light. The imagesensor 422 a may receive the exit light as an optical image. Here, atransfer lens (not shown) may be provided between the output window andthe image sensor 422 a, which transfers the optical image on thefluorescent screen onto the light receiving surface of the image sensor422 a.

Moreover, the image intensifier shown in FIG. 53 may be configured toapply an electric potential difference between the multichannel plateand the photoelectric surface, according to whether a gate signal isturned on or off. When the gate signal is turned on, the electricpotential of the photoelectric surface may be lower than the electricpotential of the input side of the multichannel plate. In this case, thephotoelectron emitted from the photoelectric surface may reach themultichannel plate by the electric potential difference. Therefore, whenthe gate signal is turned on, the photoelectron emitted from thephotoelectric surface may be multiplied by the multichannel plate, andtherefore the image sensor 422 a may receive an optical imagecorresponding to the multiplied electrons. On the other hand, when thegate signal is turned off, the electric potential of the photoelectricsurface may be higher than the electric potential of the input side ofthe multichannel plate. In this case, the photoelectron emitted from thephotoelectric surface is drawn back to the photoelectric surface, andtherefore cannot reach the multichannel plate. Therefore, when the gatesignal is turned off, the photoelectron emitted from the photoelectricsurface may not be multiplied by the multichannel plate, and thereforethe image sensor 422 a cannot receive an optical image. In this way, theimage intensifier shown in FIG. 53 may realize the shutter functionaccording to whether the gate signal is turned on or off.

Here, the shutter 422 d may be a CCD electronic shutter as long as theshutter 422 d can realize its shutter function even if plasma light isemitted. Alternatively, the shutter 422 d may be a PLZT polarizationshutter. The PLZT polarization shutter may be configured to arrange aplurality of polarizing plates in the crossed nicols direction viapiezoelectric ceramics. Then, the shutter function may be realized byapplying a voltage to the piezoelectric ceramics between the polarizingplates to change the polarization direction of the polarizing plates. Inaddition, the shutter 422 d may be realized by combining theabove-described various shutters and a mechanical shutter.

10.3 Another Modification

In the droplet detector 41, the light source part 411 and the lightreceiving part 412 may not need to face one another across the targettraveling path 272. For example, the window 411 c of the light sourcepart 411 and the window 412 c of the light receiving part 412 may bearranged to face toward the same point but not be in parallel. The lightreceiving part 412 may detect the light reflected from the droplet 271.In this way, the arrangement of the window 411 c of the light sourcepart 411 and the window 412 c of the light receiving part 412 may not belimited as long as it is possible to detect the reflected light from thedroplet 271.

With the above-described embodiments, the continuous jet method isemployed for the droplet forming mechanism 73. However, theelectrostatic suction method may be applicable. With the electrostaticsuction method, a suction electrode may be provided to be spaced fromthe nozzle hole 262 a on the target traveling path 272. Then, anelectric potential difference may be created between the suctionelectrode and the target 27 in the tank 261. By this means, it ispossible to generate an electrostatic force between the suctionelectrode and the target 27. This electrostatic force may allow thetarget 27 protruding from the nozzle hole 262 a to be divided, and thedivided target 27 may form the droplet 271 due to its surface tension.

Part or all of the EUV light generation controller 5, the shootingcontroller 81, the delay circuit 82, and the image measurement controlcircuit 83 may be combined to form as one controller.

It would be obvious to a person skilled in the art that the technologiesdescribed in the above-described embodiments including the modificationsmay be compatible with each other.

The descriptions above are intended to be illustrative only and thepresent disclosure is not limited thereto. Therefore, it will beapparent to those skilled in the art that it is possible to makemodifications to the embodiments of the present disclosure within thescope of the appended claims.

The terms used in this specification and the appended claims should beinterpreted as “non-limiting.” For example, the terms “include” and “beincluded” should be interpreted as “including the stated elements butnot limited to the stated elements.” The term “have” should beinterpreted as “having the stated elements but not limited to the statedelements.” Further, the indefinite article “one (a/an)” should beinterpreted as “at least one” or “one or more.”

REFERENCE SIGNS LIST

-   1 EUV light generation apparatus-   2 chamber-   25 plasma generation region-   25 a imaging region-   26 target supply part-   27 target-   271 droplet-   271 a secondary target-   271 b tertiary target-   31 a to 33 a main pulse laser beam-   31 b to 33 b prepulse laser beam-   31 c to 33 c first prepulse laser beam-   31 d to 33 d second prepulse laser beam-   41 droplet detector-   42, 43 image measurement unit-   422, 432 imaging part-   8 controller-   81 shooting controller-   82 delay circuit-   83 image measurement control circuit

The invention claimed is:
 1. An extreme ultraviolet light generationapparatus comprising: a chamber including a plasma generation region towhich a target is supplied, the target being turned into plasma so thatextreme ultraviolet light is generated in the chamber; a target supplypart configured to supply the target to the plasma generation region byoutputting the target as a droplet into the chamber; a droplet detectorconfigured to detect the droplet traveling from the target supply partto the plasma generation region; an imaging part configured to capturean image of an imaging region containing the plasma generation region inthe chamber; and a controller configured to control an imaging timing atwhich the imaging part captures the image of the imaging region, basedon a detection timing at which the droplet detector detects the droplet,wherein the droplet is turned into plasma upon being irradiated with alaser beam in the plasma generation region, and emits plasma lightcontaining the extreme ultraviolet light; the controller controls anirradiation timing at which the droplet is irradiated with the laserbeam in the plasma generation region, based on the detection timing; thecontroller sets a first imaging timing to a timing just after theirradiation timing; and the imaging part captures an image of the plasmalight generated in the imaging region at the first imaging timing. 2.The extreme ultraviolet light generation apparatus according to claim 1,wherein: the controller sets the irradiation timing to a timing which isdelayed from the detection timing by a predetermined period of time, andalso sets the a second imaging timing to a timing just before theirradiation timing; and the imaging part captures an image of thedroplet falling within the imaging region at the second imaging timing.3. The extreme ultraviolet light generation apparatus according to claim1, wherein the controller controls a position of the droplet and afocused position of the laser beam, based on the image of the dropletand the image of the plasma light captured by the imaging part.
 4. Anextreme ultraviolet light generation apparatus comprising: a chamberincluding a plasma generation region to which a target is supplied, thetarget being turned into plasma so that extreme ultraviolet light isgenerated in the chamber; a target supply part configured to supply thetarget to the plasma generation region by outputting the target as adroplet into the chamber; a droplet detector configured to detect thedroplet traveling from the target supply part to the plasma generationregion; an imaging part configured to capture an image of an imagingregion containing the plasma generation region in the chamber; and acontroller configured to control an imaging timing at which the imagingpart captures the image of the imaging region, based on a detectiontiming at which the droplet detector detects the droplet, wherein: afirst prepulse laser beam, a second prepulse laser beam and a main pulselaser beam are introduced into the plasma generation region; the dropletoutputted to the plasma generation region is irradiated with the firstprepulse laser beam; a secondary target resulting from irradiating thedroplet with the first prepulse laser beam is irradiated with the secondprepulse laser beam; a tertiary target resulting from irradiating thesecondary target with the second prepulse laser beam is irradiated withthe main pulse laser beam; the tertiary target is turned into plasmaupon being irradiated with the main pulse laser beam, and emits plasmalight containing the extreme ultraviolet light; the controller controlsa first irradiation timing at which the droplet is irradiated with thefirst prepulse laser beam, a second irradiation timing at which thesecondary target is irradiated with the second prepulse laser beam, anda third irradiation timing at which the tertiary target is irradiatedwith the main pulse laser beam, based on the detection timing; thecontroller sets the first irradiation timing to a timing which isdelayed from the detection timing by a first predetermined period oftime, and also sets a first imaging timing to a timing just before thefirst irradiation timing; and the imaging part captures an image of thedroplet falling within the imaging region at the first imaging timing.5. The extreme ultraviolet light generation apparatus according to claim4, wherein: the controller sets the second irradiation timing to atiming which is delayed from the detection timing by a secondpredetermined period of time longer than the first predetermined periodof time, and also sets a second imaging timing to a timing just beforethe second irradiation timing: and the imaging part captures an image ofthe secondary target falling within the imaging region at the secondimaging timing.
 6. The extreme ultraviolet light generation apparatusaccording to claim 5, wherein: the controller sets the third irradiationtiming to a timing which is delayed from the detection timing by a thirdpredetermined period of time longer than the second predetermined periodof time, and also sets a third imaging timing to a timing just beforethe third irradiation timing: and the imaging part captures an image ofthe tertiary target falling within the imaging region at the thirdimaging timing.
 7. The extreme ultraviolet light generation apparatusaccording to claim 6, wherein: the controller sets a fourth imagingtiming to a timing just after the third irradiation timing; and theimaging part captures an image of the plasma light falling withingenerated in the imaging region at the fourth imaging timing.
 8. Theextreme ultraviolet light generation apparatus according to claim 7,wherein the controller controls: a position of the droplet based on theimage of the droplet captured by the imaging part; a focused position ofthe first prepulse laser beam based on the image of the secondary targetcaptured by the imaging part; a focused position of the second prepulselaser beam based on the image of the tertiary target captured by theimaging part; and a focused position of the main pulse laser beam basedon the image of the plasma light captured by the imaging part.